Quick wins for a faster PC:
Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Use aiohttp to download the PDF, then use a PDF library such as PyMuPDF to add text to its pages. aiohttp handles the HTTP transfer; it does not edit PDFs. The example below streams a remote PDF to disk, checks the response, inserts a text watermark on each page, and saves a separate output file.
What aiohttp does—and what it does not
aiohttp is an asynchronous HTTP client. It can fetch a PDF or send a modified PDF to another service, but you need a PDF library to change page content. This guide uses PyMuPDF for direct text insertion. If your workflow already creates a separate one-page PDF containing the watermark, pypdf can instead merge that page onto each target page.
The code targets the APIs documented in aiohttp 3.14.3 and the current PyMuPDF documentation. Install the packages in your environment and test the output with your own PDFs; behavior can vary with page geometry, rotation, fonts, encryption, and unusual files.
Install the libraries
Install aiohttp and PyMuPDF in the Python environment that will run the script:
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
python -m pip install aiohttp pymupdfPyMuPDF is imported as fitz. The example uses a local temporary input file so that the complete HTTP response is not held in memory while downloading.
Download a PDF and add a text watermark
Save this as watermark_pdf.py. Replace the example URL with a PDF you are authorized to access. The script writes watermarked.pdf in the current directory and leaves the downloaded source separate.
import asyncio
import os
import tempfile
from pathlib import Path
from urllib.parse import urlparse
import aiohttp
import fitz # PyMuPDF
PDF_URL = "https://example.com/document.pdf"
OUTPUT_PATH = Path("watermarked.pdf")
WATERMARK = "CONFIDENTIAL"
CHUNK_SIZE = 64 * 1024
MAX_DOWNLOAD_BYTES = 100 * 1024 * 1024
async def download_pdf(session: aiohttp.ClientSession, url: str, destination: Path) -> None:
async with session.get(url, allow_redirects=True) as response:
response.raise_for_status()
content_type = response.headers.get("Content-Type", "").lower()
if "pdf" not in content_type and not urlparse(str(response.url)).path.lower().endswith(".pdf"):
raise ValueError(
f"Response does not appear to be a PDF "
f"(Content-Type: {content_type or 'not provided'})"
)
total = 0
with destination.open("wb") as output:
async for chunk in response.content.iter_chunked(CHUNK_SIZE):
total += len(chunk)
if total > MAX_DOWNLOAD_BYTES:
raise ValueError(f"PDF exceeds the {MAX_DOWNLOAD_BYTES}-byte download limit")
output.write(chunk)
if total == 0:
raise ValueError("The server returned an empty response")
def add_text_watermark(source: Path, destination: Path, text: str) -> None:
document = fitz.open(source)
try:
if document.is_encrypted:
raise ValueError("The PDF is encrypted; authenticate it before watermarking")
if document.page_count == 0:
raise ValueError("The PDF contains no pages")
for page in document:
# PyMuPDF page coordinates start at the top-left. Insert near the
# center; inspect and adjust for your page sizes and rotations.
rect = page.rect
point = (rect.width * 0.25, rect.height * 0.55)
page.insert_text(
point,
text,
fontsize=34,
fontname="helv",
color=(0.65, 0.65, 0.65),
overlay=True,
rotate=0,
)
# Save to a distinct file; do not overwrite the input during processing.
document.save(destination, garbage=4, deflate=True)
finally:
document.close()
async def main() -> None:
timeout = aiohttp.ClientTimeout(total=90)
headers = {"User-Agent": "PDF-watermark-script/1.0"}
# A session can be reused for related requests; it owns pooled connections.
async with aiohttp.ClientSession(timeout=timeout, headers=headers) as session:
with tempfile.TemporaryDirectory(prefix="pdf-watermark-") as temp_dir:
input_path = Path(temp_dir) / "download.pdf"
await download_pdf(session, PDF_URL, input_path)
add_text_watermark(input_path, OUTPUT_PATH, WATERMARK)
print(f"Saved watermarked PDF to {OUTPUT_PATH.resolve()}")
if __name__ == "__main__":
asyncio.run(main())Run it with python watermark_pdf.py. A successful run prints the output path. The watermark is inserted over existing page content because overlay=True; it can obscure text if placed poorly. The example uses a built-in Helvetica-style font, gray text, and a fixed point size, so review the output before using it for legal, archival, or production documents.
Choose placement and layer order deliberately
Position and page geometry
The example derives its insertion point from each page’s width and height, rather than assuming every page is US Letter or A4. Its point coordinates still need visual verification, especially for landscape pages, mixed page sizes, and rotated pages. Change the fraction values or use a layout calculation suited to your intended position. Test on representative pages, then extract or render pages for review before distributing the document.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
Foreground text versus a background watermark
With PyMuPDF’s text insertion, the overlay setting controls whether new content is placed over or under existing page content. The example uses overlay=True, a foreground mark. If you place text behind dense existing page content, the result may be difficult to see; if you place it above content, it may cover important information. Check the visual result instead of assuming a setting will be suitable for every PDF.
pypdf’s documented stamp/watermark workflow merges a one-page stamp PDF onto target pages. Its documentation says to set over=False for watermarking behind the page content and over=True for a foreground stamp. That merge example uses a PDF page as the stamp; it does not generate text. You must first create or render a page containing the desired text. See pypdf’s stamp and watermark guide.
Small PDFs, large PDFs, and memory
For a small response, aiohttp’s await response.read() returns the entire body as bytes. That can be convenient when the PDF library accepts an in-memory stream, but the full response occupies memory. The aiohttp quickstart explicitly notes that its convenience body-reading methods read the whole response into memory. For larger or untrusted downloads, streaming chunks to a file—as in the example—avoids accumulating the complete HTTP body in Python memory.
- Set a timeout appropriate to the source and your application. The example uses a 90-second total timeout; it is an example value, not a universal recommendation.
- Enforce an application-level maximum size. The example stops after 100 MiB; select a limit appropriate to your workload.
- Check HTTP status before treating the body as a PDF. A successful HTTP response can still contain HTML or another unexpected payload.
- Use a temporary directory or another cleanup strategy so partial downloads are not mistaken for complete files.
- For very large PDFs, streaming the download does not make PDF editing itself constant-memory. The PDF library still needs to parse and write the document.
Reusing a ClientSession for related requests supports connection pooling and keep-alive behavior. The example creates one session for its download; in a service processing many documents, pass a shared session through the application lifecycle rather than creating a new session for every request. See the aiohttp client reference.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Return the modified PDF to another service
After editing, aiohttp can upload the output as a request body. For a simple file upload, pass an opened file object as the request data and close it reliably. For multipart APIs, use aiohttp.FormData and set the field name, filename, and content type required by the receiving service. Consult that service’s API contract for the expected form fields and response handling.
Be careful when combining streamed uploads and redirects: aiohttp documents that a non-rewindable request body may not be replayable after a redirect. If the destination can redirect, follow its documented upload endpoint or arrange a rewindable body and handle the redirect behavior explicitly.
Troubleshoot common failures
HTTP errors, login pages, or HTML saved as a PDF
raise_for_status() raises on unsuccessful HTTP status codes, but an HTTP 200 response can still be a login page or an error page. Inspect the final response URL, status, Content-Type, and a small portion of the downloaded file when diagnosis is needed. Do not rely on the URL suffix alone; validate that the PDF library can open the downloaded file.
Watermark is missing, clipped, or misplaced
Adjust the insertion point for the page’s actual dimensions and inspect portrait, landscape, and rotated pages. Confirm the watermark is not outside the visible page rectangle and that the selected layer order does not hide it behind opaque content. The fixed position and font size in the sample are starting values, not a universal placement formula.
The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Watermark covers readable content
Move it to a less important region, reduce font size, or choose a lighter color. A text watermark can still interfere with reading even when it is gray. Review every page type that matters, including dense forms and pages with headers or footers.
Encrypted, malformed, or unusual documents fail
PyMuPDF may raise errors when opening, editing, or saving documents it cannot handle. The example explicitly rejects encrypted input rather than silently proceeding. Handle library exceptions in the calling application, keep the source intact, and report a useful failure status. The cited documentation does not establish universal behavior for every malformed, encrypted, or unusual PDF.
Upload fails after a redirect
If the outgoing request uses a stream or async generator, it may not be possible to replay the body after a redirect. Check the destination URL and upload instructions, and use the service’s final upload endpoint where possible. Avoid automatically retrying a one-shot body unless it can be safely recreated.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Or skip the browser setup
ScreenshotNeo is a website screenshot API, not a PDF text-watermarking library: it captures a web page as an image or PDF and does not add a watermark to an existing PDF. If your actual task is to capture a web page, one GET request can return a screenshot. See the ScreenshotNeo API documentation.
Recommended Free Tools
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpScreenshotNeo removes supported cookie banners, newsletter popups, and chat widgets before capture; those cleanup steps can be turned off. Bot checks, blank pages, and failed loads are not billed, and responses identify the page verdict and billing status. Its MCP server provides screenshot and PDF-capture tools for AI agents. The free plan includes 1,000 screenshots per month without a card; paid plans start at $5 for 3,000 shots.
Sign up free for 1,000 screenshots a month with no card.
Sources and implementation boundaries
- aiohttp Client Quickstart documents response body handling and streaming.
- aiohttp Client Reference documents session behavior and request details.
- pypdf 6.6.2 watermark guide covers merging a stamp page and the under/over setting.
- PyMuPDF The Basics documents page editing and coordinate concepts.
Frequently Asked Questions
Does adding a watermark with PyMuPDF alter the original PDF file?
The example saves to a separate output path and leaves its downloaded input untouched.
Can I watermark a PDF without downloading it first?
The PDF library must receive the document data, but your application can use an in-memory stream for small files or a temporary file for larger ones.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
