The Tool Desk
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You can process PDFs in a browser without sending their document bytes to a PDF-processing server: read a user-selected file locally, use PDF.js to parse and render it, and use pdf-lib for editing or creating PDFs. That architecture can support a no-document-upload claim, but it does not by itself prove that a particular deployed toolkit sends no document data—or makes no other network requests. The implementation and its live traffic need to be checked.
What “client-side” and “zero cloud uploads” mean
In a client-side workflow, the browser receives the selected PDF and performs the relevant processing on the user’s device. The file’s bytes do not need to be sent to a PDF-processing backend. This is a statement about document handling, not a guarantee that the page makes no network requests at all: the app may still load scripts or use analytics, telemetry, remote OCR, or other services. Whether any of those are present must be established for the specific application.
The title’s claim about a particular toolkit is not independently established by the available technical documentation. To make that claim responsibly, inspect the implementation and deployment, then verify the requests made during file selection, processing, and download. Documentation for the libraries establishes that local PDF processing is technically plausible; it does not verify a particular site’s behavior.
Choose separate components for viewing and editing
| Need | Suitable library | Documented capabilities |
|---|---|---|
| Parse, render, and display PDFs | PDF.js | Its architecture separates a core layer that parses and interprets PDF data, a display API for rendering and document information, and a viewer layer that provides UI. |
| Create or modify PDFs | pdf-lib | Its documented features include creating and modifying PDFs, drawing text and images, embedding fonts and pages, adding or removing pages, splitting or merging documents, and reading or filling common form fields. |
The two libraries address different parts of a toolkit rather than serving as interchangeable choices. The pdf-lib project describes its JavaScript library as usable in browsers and other JavaScript runtimes; that is the project’s compatibility statement, not a guarantee that every operation works identically in every browser or with every PDF.
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PDF.js includes a viewer layer, but Mozilla asks integrators using its generic viewer as a starting point to re-skin it or build upon it rather than embed it unchanged. The project’s prebuilt package includes pdf.mjs and pdf.worker.mjs, as well as supporting files such as character maps and viewer assets.
Build the local file-processing path
- Accept a user-selected PDF. Read the file in the browser rather than fetching it from a processing service. Keep the data in binary form for the PDF.js input path.
- Pass bytes to PDF.js. PDF.js accepts PDF data as a
Uint8Array. Its FAQ recommends passing typed-array data directly instead of converting it to base64, which uses more memory. - Render only what the user needs. Use PDF.js for parsing and display. Avoid rendering every page at high resolution when the task does not require it; the project warns that this can be resource-intensive and that some PDFs are slow.
- Apply edits with pdf-lib where appropriate. Use its documented creation and modification operations for features such as merging, splitting, page changes, or form filling. Treat each operation as a supported capability, not a promise that every input document will behave perfectly.
- Return the result to the user. Generate the output in the browser and let the user download it, without routing the document through a processing backend.
Keep the PDF.js worker matched to its library
PDF.js uses a separate worker. The library and worker should come from the same release: the PDF.js FAQ says mismatched versions are not guaranteed to work and may cause version errors. A stale cached worker is one documented cause, as is loading the library and worker from different versioned locations.
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During local development, serve the app through a local web server. The PDF.js getting-started guide says its worker is not enabled for file:// development URLs. Browser support also varies by browser and version, so check the PDF.js support information and test the specific combinations the app intends to support rather than making a universal compatibility claim.
Verify that document bytes stay in the browser
A credible privacy statement needs evidence about the actual app, not just the choice of libraries. Review the code path from file selection through processing and download, and inspect network activity while exercising those actions. Confirm that requests do not include the PDF bytes or route them to a remote processing service. Also identify what other requests the page makes, so “no document uploads” is not mistaken for “no network activity.”
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- Inspect the deployed app’s scripts and configuration, not only a local development build.
- Check requests during file selection, each processing feature, errors, and output download.
- Determine whether remote OCR, analytics, telemetry, crash reporting, or third-party scripts are used, and describe their role accurately.
- Repeat the check after deployment changes, since the privacy boundary depends on the code and services actually running.
PDF.js documents that cross-origin requests are not allowed by default under ordinary JavaScript permissions. Its FAQ describes CORS or a server proxy as ways to permit remote access. That matters if a tool fetches a PDF from a URL; it is separate from processing a file the user selected locally. A server proxy, in particular, changes where the document is handled and should be accounted for in any privacy description.
Account for memory, document behavior, and active content
There is no universal file-size limit, page-count limit, or processing speed established by the library documentation. Performance depends on the document, device resources, browser behavior, and implementation choices. High-resolution rendering of every page can consume substantial resources, and some PDFs may be slow.
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pdf-lib also documents an API for adding JavaScript that runs when a PDF is opened. That is distinct from ordinary page drawing or editing. If an application creates or handles such actions, explain their behavior and review the security implications; the library’s editing capabilities do not establish that it automatically neutralizes active content.
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PDF.js and pdf-lib provide documented building blocks for a browser-based PDF toolkit: one focuses on parsing and display, while the other supports document creation and modification. Together with local file input and browser-side output, they make it possible to design a workflow that does not upload selected document bytes to a processing server.
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Those capabilities do not establish which features a specific toolkit implements, how reliably it handles every PDF, or whether its deployed version sends document data elsewhere. Those claims require evidence from that implementation, including inspection of its code and network behavior.
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