A Base64 string is only an encoding of PDF bytes. Decode it first, then give the resulting binary data to a PDF parser and map the parser’s page text into the JSON shape your application needs. In Node.js, use Buffer.from(value, 'base64') and a buffer-capable extractor. In a browser, convert the string to a Uint8Array and pass it to PDF.js. Neither route performs OCR on an image-only scan.
This guide shows both implementations, a practical page-oriented JSON schema, handling for data-URI prefixes and memory limits, and fixes for common failures.
What the conversion actually involves
There are two separate operations:
- Decode: Base64 text becomes the original PDF bytes.
- Extract: A PDF library reads those bytes and exposes text items, page metadata, coordinates, or other document structures.
Returning JSON is your application’s design decision. A useful default is one object per page, with a page number and a single normalized text string. You can later add coordinates, raw text items, or extracted rows without changing the decoding step.
Node.js: decode a Base64 PDF and return page JSON
Install the extractor
The pdf.js-extract documentation provides extractBuffer(buffer, options, callback) and exposes page content items whose text is in item.str.
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npm install pdf.js-extractComplete example
The following function accepts either plain Base64 or a data:application/pdf;base64, value, decodes it once, and serializes one result object per page.
import { PDFExtract } from 'pdf.js-extract';
function removeDataUriPrefix(value) {
const comma = value.indexOf(',');
return value.startsWith('data:') && comma !== -1
? value.slice(comma + 1)
: value;
}
export function extractPdfJson(base64Pdf) {
const payload = removeDataUriPrefix(base64Pdf).replace(/s+/g, '');
const pdfBuffer = Buffer.from(payload, 'base64');
const extractor = new PDFExtract();
return new Promise((resolve, reject) => {
extractor.extractBuffer(pdfBuffer, {}, (error, data) => {
if (error) {
reject(error);
return;
}
const pages = data.pages.map((page) => ({
page: page.info.num,
text: page.content.map((item) => item.str).join(' ')
}));
resolve({ pages });
});
});
}
const result = await extractPdfJson(base64Pdf);
console.log(JSON.stringify(result, null, 2));Node’s Buffer documentation states that the Base64 decoder accepts the URL-safe alphabet and ignores whitespace. Stripping whitespace yourself makes input handling explicit, while Buffer.from performs the actual conversion. Validate that the decoded value is non-empty before parsing so an empty or truncated upload does not become an opaque parser error.
Typical Node output
{
"pages": [
{ "page": 1, "text": "Invoice 1042 Acme Corporation ..." },
{ "page": 2, "text": "Payment terms Net 30 ..." }
]
}The property names are not imposed by PDF.js or by the package. Rename page to pageNumber, return a combined fullText, or retain each item’s coordinates when your consumer needs layout information.
Browser: turn Base64 into a Uint8Array for PDF.js
PDF.js accepts binary document data and documents Uint8Array as the preferred representation for memory use. Its API documentation and examples show loading a document, retrieving each page, and calling getTextContent(). The project’s FAQ advises decoding Base64 before supplying the bytes.
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Browser extraction function
This example assumes your application has loaded PDF.js and made its API available as pdfjsLib. A bundler setup must also configure PDF.js’s worker as required by the version you install.
function base64ToUint8Array(input) {
const comma = input.indexOf(',');
const payload = input.startsWith('data:') && comma !== -1
? input.slice(comma + 1)
: input;
const binary = atob(payload.replace(/s+/g, ''));
const bytes = new Uint8Array(binary.length);
for (let i = 0; i < binary.length; i += 1) {
bytes[i] = binary.charCodeAt(i);
}
return bytes;
}
async function extractPdfJson(base64Pdf) {
const data = base64ToUint8Array(base64Pdf);
const loadingTask = pdfjsLib.getDocument({ data });
const pdf = await loadingTask.promise;
const pages = [];
for (let pageNumber = 1; pageNumber <= pdf.numPages; pageNumber += 1) {
const page = await pdf.getPage(pageNumber);
const textContent = await page.getTextContent();
pages.push({
page: pageNumber,
text: textContent.items.map((item) => item.str).join(' ')
});
}
return { pages };
}
const result = await extractPdfJson(base64Pdf);
console.log(JSON.stringify(result));atob() produces a binary string, so the loop copies each byte into a typed array. Do not pass the original Base64 characters as the data value; PDF.js expects decoded binary data.
When the input is a data URL
A caller may send data:application/pdf;base64,JVBERi0x... instead of the payload alone. The prefix is metadata, not part of the encoded bytes. Remove everything through the first comma before calling atob. If your API contract accepts only raw Base64, reject a data URL with a clear validation message rather than silently producing incorrect bytes.
Choose a JSON shape deliberately
There is no universal “PDF text JSON” standard. Select a shape based on what downstream code must do.
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| Use case | Suggested fields | Trade-off |
|---|---|---|
| Search or indexing | pages[].page, pages[].text |
Small and easy to consume, but layout is lost. |
| Auditing or highlighting | Page number plus each item’s str, transform, and bounding data |
Preserves locations; consumers must reconstruct lines. |
| Simple export | A single fullText string |
Convenient for prompts and logs, but page boundaries disappear. |
| Table-oriented processing | Page text items grouped into lines or rows | Useful for known templates; grouping is not guaranteed semantic table recognition. |
pdf.js-extract exposes coordinates and row-grouping utilities, but inspect representative documents before treating a grouped row as a real table record. Columns, headers, and reading order vary between PDFs.
Handling difficult input
Scanned or image-only PDFs
Text extraction reads a PDF’s text layer. The pdf.js-extract package explicitly states “NO OCR!” A scan made from page images can therefore produce empty strings even though a person can see words on the page. Add a separate OCR stage, retain the page images, and mark OCR-derived text differently if accuracy matters. Do not report an empty extraction as proof that the document contains no text until you have checked whether it is image-only.
Password-protected files
PDF.js’s API includes a password-loading parameter. Your application must obtain the password and provide it through the parser’s supported mechanism. Encryption compatibility and error wording depend on the library and document, so surface a specific “password required” state instead of retrying indefinitely.
Malformed or unsupported PDFs
Catch parser errors around the extraction call. Preserve an input identifier and byte length, return a stable application error such as PDF_PARSE_FAILED, and avoid returning partially assembled JSON as if it were complete. Test the exact classes of PDFs your service receives; no parser guarantees success for every malformed or feature-rich file.
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Tables, columns, and reading order
Text items commonly include positions, but concatenating them in array order can interleave columns or separate labels from values. For reliable layout-sensitive processing, keep the item coordinates, group by page and line, and add document-specific sorting rules. A visual table is not automatically a semantic table.
Memory and performance considerations
Base64 expands binary data and decoding can temporarily create more than one copy in memory. The PDF.js FAQ recommends supplying raw binary data as a typed array when possible. If an upstream system already gives you Base64, decode it once, release the original string when safe, and avoid converting the bytes back to Base64 between parsing steps.
- Set an input-size limit before decoding to protect browser tabs and server processes.
- Process pages incrementally when your parser permits it instead of retaining every intermediate object.
- Return page results progressively or store them in a bounded queue for very large documents.
- Normalize whitespace only after extraction; premature normalization can hide missing text or alter meaningful spacing.
No benchmark is implied by these practices. Actual throughput depends on page count, embedded fonts and images, parser version, available memory, and whether OCR is added.
Browser PDF.js, Node.js, or a viewer SDK?
| Option | Runtime | Input path | Best fit | OCR included? |
|---|---|---|---|---|
| PDF.js | Browser | Decode to typed-array binary and call getDocument |
Client-side viewing and page text | Not established as included by the cited API material |
| Node.js plus pdf.js-extract | Node.js | Buffer.from, then extractBuffer |
Server-side extraction, coordinates, and custom JSON | No; the package says “NO OCR!” |
| PDF.js Express | Browser viewer SDK | Vendor documents Base64-to-Blob loading | Applications needing broader viewer/document operations | Not established by the cited Base64 page |
PDF.js is an open-source project. PDF.js Express is described in its Base64 documentation as a commercial SDK; it is not required for ordinary text extraction.
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Troubleshooting checklist
| Symptom | Likely cause | Fix |
|---|---|---|
| “Invalid PDF” immediately after decoding | The data-URL prefix, whitespace, or a JSON wrapper was passed as payload. | Extract the value, remove the prefix, strip whitespace, and verify the decoded bytes begin with a valid PDF header. |
atob throws a decoding error |
The browser received URL-safe characters, corrupted text, or non-Base64 input. | Validate the producer’s encoding contract and reject malformed input before calling atob. |
| Every page has empty text | The PDF is scanned or has no usable text layer. | Inspect the file visually and add OCR for image-only pages. |
| Words appear in the wrong order | Multiple columns or positioned text items were joined without layout rules. | Retain coordinates and implement page-specific line and column grouping. |
| Password prompt or encryption error | The file is protected. | Collect the password and pass it through the parser’s documented password option. |
| Browser tab or process runs out of memory | Large Base64 strings and duplicate byte arrays remain live. | Limit input size, decode once, release references, and process pages incrementally. |
| Node callback reports an extraction error | The PDF is malformed, unsupported, or the installed package API differs. | Log the library version, test the file independently, and consult the installed package documentation before changing the callback or options. |
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curl -G 'https://api.screenshotneo.com/v1/shot' -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpThe same request from Python:
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r.raise_for_status()
open('shot.webp', 'wb').write(r.content)And from Node.js:
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const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
if (!res.ok) throw new Error(`HTTP ${res.status}`);
const data = Buffer.from(await res.arrayBuffer());
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Operational practices for production services
- Define whether your endpoint accepts raw Base64, a data URL, or both, and document the maximum decoded byte size.
- Return a stable schema with a parser status, page count, and per-page results so callers can distinguish an empty page from a failed extraction.
- Keep parser errors separate from OCR errors; they require different remediation and monitoring.
- Use fixture PDFs representing text, columns, tables, scans, encryption, and malformed input. Compare normalized expected JSON in automated tests.
- Apply access controls to uploaded PDFs and avoid logging raw Base64, which can contain confidential document content.
FAQ
Can I change PDF libraries without changing my API?
Yes. Keep your public page-oriented schema in an adapter layer. Each parser maps its own page and text-item structures into that contract, allowing library upgrades or runtime changes without forcing every client to rewrite its JSON handling.
What should regression tests compare?
Store representative PDFs with expected page counts and normalized page text. Add separate assertions for coordinates or row grouping when layout matters, because those details can change independently of the decoded bytes.
Frequently Asked Questions
Can I change PDF libraries without changing my API?
Yes. Keep your public page-oriented schema in an adapter layer. Each parser maps its own page and text-item structures into that contract, allowing library upgrades or runtime changes without forcing every client to rewrite its JSON handling.
What should regression tests compare?
Store representative PDFs with expected page counts and normalized page text. Add separate assertions for coordinates or row grouping when layout matters, because those details can change independently of the decoded bytes.
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