Ultimate PDF Transformation Guide: Local Processing for Pros

1import { PDFDocument } from 'pdf-lib';
2 
3async function splitPDF(file: File): Promise<Blob[]> {
4  const arrayBuffer = await file.arrayBuffer();
5  const sourcePdf = await PDFDocument.load(arrayBuffer);
6  const pageCount = sourcePdf.getPageCount();
7  const pages: Blob[] = [];
8 
9  for (let i = 0; i < pageCount; i++) {
10    // Create a new single-page document for each page
11    const singlePageDoc = await PDFDocument.create();
12    const [copiedPage] = await singlePageDoc.copyPages(sourcePdf, [i]);
13    singlePageDoc.addPage(copiedPage);
14 
15    const bytes = await singlePageDoc.save();
16    pages.push(new Blob([bytes], { type: 'application/pdf' }));
17  }
18 
19  return pages; // Array of single-page PDF Blobs
20}
21 
22// Download all pages as separate files
23const pageBlobs = await splitPDF(file);
24pageBlobs.forEach((blob, index) => {
25  const url = URL.createObjectURL(blob);
26  const link = document.createElement('a');
27  link.href = url;
28  link.download = `page-${index + 1}.pdf`;
29  link.click();
30  URL.revokeObjectURL(url);
31});

1import { PDFDocument, degrees } from 'pdf-lib';
2 
3async function rotatePDFPages(
4  file: File,
5  pageIndices: number[],  // Which pages to rotate (0-indexed)
6  rotation: 90 | 180 | 270  // Rotation in degrees
7): Promise<Blob> {
8  const arrayBuffer = await file.arrayBuffer();
9  const pdfDoc = await PDFDocument.load(arrayBuffer);
10 
11  pageIndices.forEach(index => {
12    const page = pdfDoc.getPage(index);
13    const currentRotation = page.getRotation().angle;
14    // Add to existing rotation (in case page was already rotated)
15    page.setRotation(degrees((currentRotation + rotation) % 360));
16  });
17 
18  const bytes = await pdfDoc.save();
19  return new Blob([bytes], { type: 'application/pdf' });
20}
21 
22// Rotate only page 1 (index 0) by 90 degrees clockwise
23const rotated = await rotatePDFPages(file, [0], 90);

1import * as pdfjsLib from 'pdfjs-dist';
2 
3// Required: set the worker URL (use a CDN or bundle the worker separately)
4pdfjsLib.GlobalWorkerOptions.workerSrc =
5  'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js';
6 
7async function extractTextFromPDF(file: File): Promise<string> {
8  const arrayBuffer = await file.arrayBuffer();
9  const pdfDoc = await pdfjsLib.getDocument({ data: arrayBuffer }).promise;
10  const pageCount = pdfDoc.numPages;
11  const textPages: string[] = [];
12 
13  for (let i = 1; i <= pageCount; i++) {
14    const page = await pdfDoc.getPage(i);
15    const textContent = await page.getTextContent();
16 
17    // Concatenate text items — maintain word spacing
18    const pageText = textContent.items
19      .map((item: pdfjsLib.TextItem | pdfjsLib.TextMarkedContent) => {
20        if ('str' in item) return item.str;
21        return '';
22      })
23      .join(' ');
24 
25    textPages.push(`--- Page ${i} ---
26${pageText}`);
27  }
28 
29  return textPages.join('
30 
31');
32}
33 
34const text = await extractTextFromPDF(file);
35console.log(text); // Full document text, page by page

1// In the main thread: send file to worker
2const worker = new Worker('/pdf-thumbnail-worker.js');
3const arrayBuffer = await file.arrayBuffer();
4worker.postMessage({ buffer: arrayBuffer, pageIndex: 0 }, [arrayBuffer]);
5 
6worker.onmessage = (e) => {
7  const { thumbnailBlob } = e.data;
8  const img = document.createElement('img');
9  img.src = URL.createObjectURL(thumbnailBlob);
10  document.body.appendChild(img);
11};
12 
13// In pdf-thumbnail-worker.js:
14importScripts('https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.min.js');
15pdfjsLib.GlobalWorkerOptions.workerSrc = ''; // Already in a worker
16 
17self.onmessage = async ({ data: { buffer, pageIndex } }) => {
18  const pdf = await pdfjsLib.getDocument({ data: buffer }).promise;
19  const page = await pdf.getPage(pageIndex + 1);
20  const viewport = page.getViewport({ scale: 0.5 }); // 50% size thumbnail
21 
22  // OffscreenCanvas avoids main-thread paint blocking
23  const canvas = new OffscreenCanvas(viewport.width, viewport.height);
24  await page.render({ canvasContext: canvas.getContext('2d'), viewport }).promise;
25 
26  const blob = await canvas.convertToBlob({ type: 'image/webp', quality: 0.85 });
27  self.postMessage({ thumbnailBlob: blob }, []);
28};

1// Handle password-protected PDFs with PDF.js
2try {
3  const pdfDoc = await pdfjsLib.getDocument({
4    data: arrayBuffer,
5    password: userPassword, // If you have it
6  }).promise;
7} catch (err) {
8  if (err instanceof pdfjsLib.PasswordException) {
9    if (err.code === pdfjsLib.PasswordResponses.NEED_PASSWORD) {
10      // Prompt user for password
11    } else if (err.code === pdfjsLib.PasswordResponses.INCORRECT_PASSWORD) {
12      // Wrong password
13    }
14  }
15}

1# Linearise a PDF using qpdf (free, cross-platform)
2qpdf --linearize input.pdf output-linearised.pdf
3 
4# Linearise with Ghostscript
5gs -dBATCH -dNOPAUSE -sDEVICE=pdfwrite \
6   -dFastWebView=true \
7   -sOutputFile=output-linearised.pdf input.pdf