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Architecture Engineering PDF/A WebAssembly

How Client-Side PDF/A Conversion Works

A deep dive into browser-based PDF parsing, sRGB ICC profile injection, and ISO 19005 compliance verification.

PDFAfy Logo PDFAfy Engineering
• • 7 min read

Most online file conversion tools upload user documents to remote cloud servers, run server-side tools (like Ghostscript or pdf2pdfa), and stream the output back. While effective, this model creates data privacy risks and server latency.

PDFAfy takes a different approach: 100% Client-Side In-Browser Conversion. Here is a technical breakdown of how our engine transforms PDFs into ISO-compliant PDF/A files directly inside your browser memory session.

The 4-Step Conversion Pipeline

Step 1: Binary Buffer Parsing

When you select a file, the browser reads its ArrayBuffer into local JavaScript memory. Our parser analyzes the %PDF- header, xref cross-reference tables, and indirect object dictionary catalog without uploading a single byte to external servers.

Step 2: XMP Metadata Packet Injection

ISO 19005 requires a valid XML XMP metadata packet embedded at /Catalog /Metadata. PDFAfy generates and injects structured RDF metadata containing:

  • pdfaid:part (1, 2, or 3)
  • pdfaid:conformance (B)
  • Synchronized dc:title, dc:creator, and dc:description matching the PDF Information dictionary.

Step 3: sRGB OutputIntent & Color Space Mapping

To eliminate device-dependent color ambiguities, PDFAfy embeds a standardized 3,144-byte sRGB IEC61966-2.1 ICC Profile stream into the document catalog under /OutputIntents (GTS_PDFA1).

Step 4: Object Sanitization & Font Embedding

Our sanitizer iterates through all indirect document dictionaries:

  • Sets the /F 4 (Print flag) on all Annotation dictionaries (/Annot, /Link, /Widget).
  • Attaches embedded TrueType binary font streams (/FontFile2) and /CIDSet streams for missing font descriptors.
  • Enforces transparency rules for PDF/A-1b or builds transparency page groups (/Group) for PDF/A-2b.

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