ISO Standards

phpdftk supports every major PDF subset standard — 7 ISO specifications plus ZUGFeRD, covering 31 conformance levels. Each is validated end-to-end in CI with dedicated integration tests and external tool verification via veraPDF, Matterhorn Protocol, and JHOVE.

At a glance

Standard	ISO	Purpose	Levels
PDF/A	19005	Long-term archival	11
PDF/UA	14289	Universal accessibility	2
PDF/X	15930	Print production	6
PDF/VT	16612	Variable/transactional printing	3
PDF/E	24517	Engineering documents	1
PDF/R	23504	Raster image transport	1
Factur-X	ZUGFeRD	E-invoicing	6
PDF/mail	23053	Email-safe documents	1

PDF/A — Long-Term Archival

ISO 19005 (Parts 1–4) ensures documents remain readable decades from now by eliminating external dependencies.

Profiles

Level	Part	PDF	Key requirements
A-1a	1	1.4	Tagged, no transparency, no encryption, all fonts embedded
A-1b	1	1.4	Visual reproduction only (no tagged requirement)
A-2a/b/u	2	1.7	Transparency allowed, JPEG2000 allowed
A-3a/b/u	3	1.7	Embedded files allowed (e.g., for invoices)
A-4/4e/4f	4	2.0	Full PDF 2.0 feature set

What gets enforced

All fonts must be embedded with complete glyph programs
No encryption permitted
XMP metadata with pdfaid identification required
OutputIntent with ICC profile required
Device-dependent color spaces trigger warnings
JavaScript, Launch, Movie, Sound actions prohibited
LZW compression prohibited (A-1 only)
Transparency prohibited (A-1 only)
Tagged structure required (Level A only)

use Phpdftk\Pdf\Conformance\Profile\PdfAProfile;

$writer->setConformance(PdfAProfile::A2b);

PDF/UA — Universal Accessibility

ISO 14289 ensures documents are accessible to users of assistive technologies.

Profiles

Level	Part	PDF
UA-1	1	1.7
UA-2	2	2.0

What gets enforced

Complete tagged structure (StructTreeRoot, StructElem hierarchy)
Document language (/Lang) required
DisplayDocTitle must be true in ViewerPreferences
All pages with annotations must have /Tabs /S
Annotations must have /Contents for accessibility (Widget/Popup exempt)
All fonts embedded
XMP metadata with pdfuaid identification

use Phpdftk\Pdf\Conformance\Profile\PdfUaProfile;

$writer->setConformance(PdfUaProfile::UA1);

Dual profile — combine with PDF/A for archival + accessible:

$writer->setConformanceProfiles([PdfAProfile::A2a, PdfUaProfile::UA1]);

PDF/X — Print Production

ISO 15930 ensures reliable color reproduction in print workflows.

Profiles

Level	Part	PDF	Transparency	External refs
X-1a:2003	4	1.3	Prohibited	No
X-3:2003	6	1.3	Prohibited	No
X-4	7	1.6	Allowed	No
X-5g/5pg/5n	8–9	1.6	Allowed	Reference XObjects

What gets enforced

OutputIntent required (GTS_PDFX type)
TrimBox or ArtBox required on every page
/Trapped must be True or False (not Unknown)
All fonts embedded
No encryption
Transparency prohibited for X-1a and X-3
Reference XObject support validated for X-5

use Phpdftk\Pdf\Conformance\Profile\PdfXProfile;

$writer->setConformance(PdfXProfile::X4);

PDF/VT — Variable & Transactional Printing

ISO 16612 (Parts 2–3) builds on PDF/X-4 for high-volume variable data printing (bills, statements, direct mail).

Profiles

Level	PDF	Description
VT-1	2.0	Single-file exchange
VT-2	2.0	Multi-file streaming
VT-2s	2.0	Streamed subset

What gets enforced

All PDF/X-4 constraints plus:

DPartRoot required (document part hierarchy for variable records)
XMP pdfvtid identification

use Phpdftk\Pdf\Conformance\Profile\PdfVtProfile;

$writer->setConformance(PdfVtProfile::VT1);

PDF/E — Engineering Documents

ISO 24517-1 supports 3D models, geospatial data, and interactive engineering content.

What gets enforced

3D content must use valid U3D or PRC streams with defined views
JavaScript and Launch actions prohibited
OutputIntent recommended (warning if missing)
All fonts embedded, no encryption
XMP metadata with identification

use Phpdftk\Pdf\Conformance\Profile\PdfEProfile;

$writer->setConformance(PdfEProfile::E1);

PDF/R — Raster Image Transport

ISO 23504-1 is designed for scanned document workflows where raster content is primary.

What gets enforced

Raster-only content expected (non-raster triggers warning)
JavaScript and Launch actions prohibited
Font presence triggers warning (raster docs shouldn’t need text fonts)
No encryption

use Phpdftk\Pdf\Conformance\Profile\PdfRProfile;

$writer->setConformance(PdfRProfile::R1);

Factur-X / ZUGFeRD — E-Invoicing

Built on PDF/A-3b, these profiles add structured invoice data as an embedded XML file.

Profiles

Level	Description
MINIMUM	Minimal machine-readable data
BASIC_WL	Basic without line items
BASIC	Standard invoice data
EN16931	EU Directive 2014/55/EU compliant
EXTENDED	Rich invoice data
XRECHNUNG	German public sector

What gets enforced

All PDF/A-3b constraints plus:

XML invoice file embedded via FileSpec/EmbeddedFile (named factur-x.xml or xrechnung.xml)
Factur-X XMP metadata with conformance level identification

use Phpdftk\Pdf\Conformance\Profile\ZugferdProfile;

$writer->setConformance(ZugferdProfile::EN16931);

PDF/mail — Email-Safe Documents

ISO 23053-2 ensures documents can be safely attached to and opened from email without triggering security concerns.

What gets enforced

No encryption
No JavaScript or Launch actions
No interactive forms (AcroForm)
No multimedia content
All fonts embedded
Pins to PDF 2.0

use Phpdftk\Pdf\Conformance\Profile\PdfMailProfile;

$writer->setConformance(PdfMailProfile::Mail1);

Constraint matrix

Shows which rules apply to which standard families.

Constraint	A	UA	X	VT	E	R	ZUGFeRD	mail
Font embedding	All	All	All	All	All	—	All	All
Encryption prohibited	All	—	All	All	All	All	All	All
XMP metadata	All	All	All	All	All	All	All	All
OutputIntent	All	—	All	All	Warn	—	All	—
Color space checks	All	—	—	—	—	—	All	—
Action restrictions	All	—	—	—	All	All	All	All
Tagged structure	Level A	All	—	—	—	—	Level A	—
Transparency	A-1 only	—	X-1a/X-3	—	—	—	A-1 only	—
TrimBox	—	—	All	All	—	—	—	—
Trapped flag	—	—	All	All	—	—	—	—
DPartRoot	—	—	—	All	—	—	—	—
3D content	—	—	—	—	Required	—	—	—
Forms prohibited	—	—	—	—	—	—	—	All
Multimedia prohibited	—	—	—	—	—	—	—	All