PDF/A is a specialized, ISO-standardized version of the Portable Document Format (PDF) specifically designed for the long-term preservation and archiving of electronic documents. It ensures that files remain accessible, readable, and true to their original appearance by embedding all necessary fonts, images, and metadata within the document itself. By adhering to strict guidelines and minimizing dependencies on external resources or proprietary software, PDF/A ensures the consistent and reliable reproduction of content, safeguarding it against future technological changes and obsolescence.
PDF/A-1: Based on PDF 1.4, PDF/A-1 is the first version of the standard and is divided into two levels: PDF/A-1a (Level A, ensuring accessibility) and PDF/A-1b (Level B, ensuring visual preservation).
Level B (Basic): Ensures visual preservation and basic requirements for archiving.
Level A (Accessible): Everything from level B, but includes additional requirements for accessibility, such as tagging, Unicode character mapping, and logical structure.
PDF/A-2: Based on PDF 1.7 (ISO 32000-1), PDF/A-2 adds features and improvements over PDF/A-1, while maintaining compatibility with PDF/A-1b (Level B) documents.
Level B (Basic): Like PDF/A-1b, but support for PDF 1.7 features such as transparancy layers.
Level U (Unicode): Ensures Unicode mapping without the full accessibility requirements of PDF/A-1a (Level A).
Level A (Accessible): Similar to PDF/A-1a
PDF/A-3: Based on PDF 1.7 (ISO 32000-1), PDF/A-3 is similar to PDF/A-2 but allows the embedding of non-PDF/A files as attachments, enabling the archiving of source or supplementary data alongside the PDF/A document. This is interesting for invoices which can add XML files.
PDF/A-4: Based on PDF 2.0 (ISO 32000-2), PDF/A-4 introduces new features and improvements for better archiving and accessibility. The previous levels are replaced by PDF/A-4f (ensuring visual preservation and allowing attachments) and PDF/A-4e (Engineering, allows 3D content).
In contrast to other PDF documents, PDF/A-1b documents must fulfill those requirements:
MarkInfo Object: The MarkInfo object is a dictionary object within a PDF/A file that provides information about the logical structure and tagging of the document. The MarkInfo object indicates whether the document is tagged, contains optional content, or has a structure tree that describes the logical arrangement of content such as headings, paragraphs, lists, and tables. By including the MarkInfo object, PDF/A ensures that electronic documents are accessible to users with disabilities, such as those using screen readers or other assistive technologies.
Embedded fonts: All fonts used in the document must be embedded to ensure consistent text rendering across different devices and systems.
Color Spaces: DeviceRGB is a device-dependent color space that relies on the specific characteristics of the output device, which can lead to inconsistent color rendering across various devices. To achieve accurate and consistent color representation, PDF/A requires the use of device-independent color spaces, such as ICC-based color profiles.
XMP (Extensible Metadata Platform) metadata: XMP metadata provides a standardized and extensible way to store essential information about a document and its properties. XMP metadata is an XML-based format embedded directly within a PDF/A file. It contains various types of information, such as document title, author, creation and modification dates, keywords, and copyright information, as well as PDF/A-specific details like conformance level and OutputIntent.
VeraPDF is the go-to PDF/A validator.
There are several online-validators which allow you to simply upload the document:
pypdf and PDF/A
At the moment, pypdf does not make any guarantees regarding PDF/A. Support is very welcome.