Save Documents

This guide explains how to save PDF documents and the available save options.

Basic Save

// Save existing document
using document = await pdfium.openDocument(data);
const bytes = document.save();
await fs.writeFile('output.pdf', bytes);

// Save new document
using builder = pdfium.createDocument();
// ... add content ...
const bytes = builder.save();
await fs.writeFile('output.pdf', bytes);

Save Options

Both PDFiumDocument.save() and PDFiumDocumentBuilder.save() accept options:

interface SaveOptions {
  flags?: SaveFlags;
  version?: number;
}

SaveFlags

import { SaveFlags } from '@scaryterry/pdfium';

Flag	Value	Description
None	0	Default full save
Incremental	1	Append changes (preserves signatures)
NoIncremental	2	Force full rewrite
RemoveSecurity	3	Remove encryption

PDF Version

Specify the PDF version as a number:

Version	Value	Released
PDF 1.4	14	2001
PDF 1.5	15	2003
PDF 1.6	16	2004
PDF 1.7	17	2006
PDF 2.0	20	2017

Save Modes Explained

Default Save (None)

Rewrites the entire PDF:

const bytes = document.save();
// or
const bytes = document.save({ flags: SaveFlags.None });

Characteristics:

• Creates optimised file
• May invalidate digital signatures
• Removes document history
• Usually smaller file size

Incremental Save

Appends changes to the end of the file:

const bytes = document.save({ flags: SaveFlags.Incremental });

Characteristics:

• Preserves digital signatures
• Maintains document history
• Faster for large documents with small changes
• File size grows with each save

Use when:

• Document has digital signatures
• Audit trail is required
• Making small modifications

Force Non-Incremental

Forces full rewrite even if incremental would be possible:

const bytes = document.save({ flags: SaveFlags.NoIncremental });

Remove Security

Removes encryption (requires correct password to open first):

// Open with password
using document = await pdfium.openDocument(data, { password: 'secret' });

// Save without encryption
const bytes = document.save({ flags: SaveFlags.RemoveSecurity });

Caution

Only use RemoveSecurity when you have legitimate rights to the document and appropriate authorisation.

Specifying PDF Version

// Save as PDF 1.7
const bytes = document.save({ version: 17 });

// Save as PDF 2.0
const bytes = document.save({ version: 20 });

Version Compatibility

Feature	Minimum Version
Basic PDF	1.4
Compressed objects	1.5
AES encryption	1.6
PDF/A-2	1.7
New annotation types	2.0

Error Handling

import { DocumentError, PDFiumErrorCode } from '@scaryterry/pdfium';

try {
  const bytes = document.save();
  await fs.writeFile('output.pdf', bytes);
} catch (error) {
  if (error instanceof DocumentError) {
    if (error.code === PDFiumErrorCode.DOC_SAVE_FAILED) {
      console.error('Failed to save document:', error.message);
    }
  }
  throw error;
}

Save to Different Formats

Save to Buffer

const bytes = document.save();
// bytes is Uint8Array

Save to File

import { promises as fs } from 'fs';

const bytes = document.save();
await fs.writeFile('output.pdf', bytes);

Save to Stream

import { createWriteStream } from 'fs';

const bytes = document.save();
const stream = createWriteStream('output.pdf');
stream.write(bytes);
stream.end();

Send as HTTP Response (Node.js)

// Express.js example
app.get('/download', async (req, res) => {
  const data = await fs.readFile('document.pdf');

  using pdfium = await PDFium.init();
  using document = await pdfium.openDocument(data);

  // Modify document...

  const bytes = document.save();

  res.setHeader('Content-Type', 'application/pdf');
  res.setHeader('Content-Disposition', 'attachment; filename="output.pdf"');
  res.send(Buffer.from(bytes));
});

Browser Download

function downloadPDF(bytes: Uint8Array, filename: string) {
  const blob = new Blob([bytes], { type: 'application/pdf' });
  const url = URL.createObjectURL(blob);

  const link = document.createElement('a');
  link.href = url;
  link.download = filename;
  link.click();

  URL.revokeObjectURL(url);
}

// Usage
const bytes = document.save();
downloadPDF(bytes, 'output.pdf');

Complete Examples

Copy with Version Update

import { PDFium } from '@scaryterry/pdfium';
import { promises as fs } from 'fs';

async function upgradePDFVersion(inputPath: string, outputPath: string) {
  const data = await fs.readFile(inputPath);

  using pdfium = await PDFium.init();
  using document = await pdfium.openDocument(data);

  // Save as PDF 1.7
  const bytes = document.save({ version: 17 });
  await fs.writeFile(outputPath, bytes);

  console.log(`Upgraded ${inputPath} to PDF 1.7`);
}

Remove Password Protection

async function removePassword(
  inputPath: string,
  outputPath: string,
  password: string
) {
  const data = await fs.readFile(inputPath);

  using pdfium = await PDFium.init();
  using document = await pdfium.openDocument(data, { password });

  const bytes = document.save({ flags: SaveFlags.RemoveSecurity });
  await fs.writeFile(outputPath, bytes);

  console.log('Password protection removed');
}

Incremental Save Workflow

async function signaturePreservingSave(
  inputPath: string,
  outputPath: string
) {
  const data = await fs.readFile(inputPath);

  using pdfium = await PDFium.init();
  using document = await pdfium.openDocument(data);

  // Make modifications here...

  // Save incrementally to preserve signatures
  const bytes = document.save({ flags: SaveFlags.Incremental });
  await fs.writeFile(outputPath, bytes);

  console.log('Saved with signatures preserved');
}

Batch Processing

import { promises as fs } from 'fs';
import path from 'path';

async function convertPDFVersions(
  inputDir: string,
  outputDir: string,
  targetVersion: number
) {
  using pdfium = await PDFium.init();

  const files = await fs.readdir(inputDir);
  const pdfFiles = files.filter(f => f.toLowerCase().endsWith('.pdf'));

  await fs.mkdir(outputDir, { recursive: true });

  for (const file of pdfFiles) {
    const inputPath = path.join(inputDir, file);
    const outputPath = path.join(outputDir, file);

    try {
      const data = await fs.readFile(inputPath);
      using document = await pdfium.openDocument(data);

      const bytes = document.save({ version: targetVersion });
      await fs.writeFile(outputPath, bytes);

      console.log(`Converted: ${file}`);
    } catch (error) {
      console.error(`Failed: ${file}`, error);
    }
  }
}

// Convert all PDFs to version 1.7
convertPDFVersions('./input', './output', 17);

See Also

• PDFiumDocument — Document API reference
• PDFiumDocumentBuilder — Creating documents
• SaveFlags Enum — Save flags reference
• Open Document Guide — Loading documents