1. The Problem With Regular PDFs in Long-Term Storage
Most developers and legal professionals assume that a PDF is an immutable snapshot of a document. In reality, standard PDFs created under ISO 32000-1 are highly dynamic execution containers. A standard PDF can query the operating system for missing fonts, execute ECMAScript for interactive form validations, stream remote audio/video payloads, and render colors using raw device-dependent RGB values without color profile anchors.
When you reopen that document twenty years later on a different operating system, catastrophic rendering discrepancies occur:
- Font Substitution Glitches: If the original authoring machine had Helvetica Neue installed with custom kerning tables and the viewing machine substitutes Arial, text reflows, page pagination changes, and signatures or stamp annotations become displaced.
- Color Shift: Without an embedded ICC (International Color Consortium) profile, RGB values render according to the physical characteristics of the display monitor, shifting legal seal colors or trademark proofs.
- Script Failure & Security Blocks: Modern PDF readers automatically disable embedded JavaScript due to malware vectors, breaking custom calculations or dynamic fields in old contracts.
To eliminate these variables, the International Organization for Standardization developed ISO 19005 (PDF/A) — a specialized subset of PDF designed for absolute, deterministic visual and semantic preservation.
2. Chronological Standards: PDF/A-1 vs PDF/A-2 vs PDF/A-3
The standard has evolved across three major revisions. Each revision builds upon a newer version of the underlying Adobe PDF specification while maintaining strict preservation rules:
| Part | ISO Standard | Underlying Base | Key Features Introduced | Ideal Use Case |
|---|---|---|---|---|
| PDF/A-1 | ISO 19005-1 (2005) | PDF 1.4 | Baseline preservation. Strictly forbids transparency, layers, and attachments. | Legacy court filings and historical institutional archiving. |
| PDF/A-2 | ISO 19005-2 (2011) | ISO 32000-1 (PDF 1.7) | Adds JPEG2000 image compression, native transparency blend modes, embedded PDF/A attachments, and PAdES digital signatures. | Modern corporate document archives, complex graphics, and engineering drawings. |
| PDF/A-3 | ISO 19005-3 (2012) | ISO 32000-1 (PDF 1.7) | Allows embedding of any arbitrary file format (XML, CSV, CAD DWG, Excel spreadsheets) as associated attachments. | E-Invoicing (ZUGFeRD, Factur-X), medical records with raw sensor data, legal briefs with raw evidence. |
3. Conformance Levels Explained: a, b, and u
When selecting a target conformance during conversion, you must specify the level of compliance required by your receiving authority:
Level b (Basic Visual Conformance)
This is the most common and achievable level for scanned documents and legacy digitizations. It mandates that the document will display visually identically across any compliant reader on any future hardware. It requires complete font glyph embedding, embedded color profiles, and the elimination of forbidden features, but does not require semantic tagging or structure trees.
Level u (Unicode Conformance)
Introduced in PDF/A-2, Level u includes all requirements of Level b, but adds a strict mandate that every single character rendered in the document must map to a definite Unicode code point. This guarantees that future search engines, text extractors, and screen readers can accurately copy, index, and search the text without encountering unmapped font ligatures or gibberish character codes.
Level a (Accessible Conformance)
Level a is the highest and most rigorous tier. In addition to visual preservation and Unicode mapping, it mandates a complete logical structural tree (similar to semantic HTML). Headers (<H1>, <H2>), paragraphs (<P>), tables (<Table>, <TR>, <TD>), and alternative text for raster illustrations (/Alt) must be mathematically tagged in the structural dictionary. This ensures accessibility for assistive screen readers under WCAG 2.1 and US Section 508.
4. What ISO 19005 Strictly Forbids
To guarantee longevity, PDF/A parsers reject documents containing any of the following elements:
- Audio and Video Content: Multimedia streams require hardware codecs and external media players that are guaranteed to become obsolete.
- JavaScript and Executable Actions: Scripts introduce non-deterministic document states and security vulnerabilities.
- Password Encryption: Files cannot have user or owner access passwords (
/Encryptdictionary). An archival repository cannot preserve a file if the cryptographic key is forgotten or deprecated. - External Font References: Every font used must be 100% embedded (or an embedded font subset containing all glyphs used) directly within the
/FontFilestream. - Device-Dependent Color Without Output Intent: An
/OutputIntentsdictionary with an embedded ICC profile (such as sRGB IEC61966-2.1 or ISO Coated v2) must be present in the document catalog. - LZW Compression: Due to historical patent uncertainties, PDF/A-1 forbids LZW compression, mandating FlateDecode (Deflate).
5. How to Validate PDF/A Compliance
Creating a valid PDF/A requires more than renaming a file or setting an XMP metadata flag. Verification engines like VeraPDF (the official open-source validator of the PDF Association and European Commission) parse the low-level object tree to inspect:
- XMP Metadata: The
pdfaid:partandpdfaid:conformanceschema fields in the catalog's metadata stream must match the physical structure. - Glyph Width Consistency: The glyph widths in the font program must match the
/Widthsarray defined in the PDF font dictionary to within 1/1000th of an em unit. - Color Space Integrity: Any transparency group (in PDF/A-2/3) must specify an isolated blending color space.
When preparing documents for European court submissions or US Federal PACER filings, converting your working PDFs through QuickRectify's PDF to PDF/A conversion utility ensures that all font tables are embedded and non-conforming interactive elements are stripped cleanly without loss of visual layout.