Description
The Standard does not define an archiving strategy or the goals of an archiving system. It identifies a "profile" for electronic documents that ensures the documents can be reproduced exactly the same way in years to come. A key element to this reproducibility is the requirement for PDF/A documents to be 100% self-contained. All of the information necessary for displaying the document in the same manner every time is embedded in the file. This includes, but is not limited to, all content (text, raster images and vector graphics), fonts, and color information. A PDF/A document is not permitted to be reliant on information from external sources (e.g. font programs and hyperlinks).
Other key elements to PDF/A compatibility include:
- Audio and video content are forbidden.
- JavaScript and executable file launches are forbidden.
- All fonts must be embedded and also must be legally embeddable for unlimited, universal rendering. This also applies to the so-called PostScript standard fonts such as Times or Helvetica.
- Colorspaces specified in a device-independent manner.
- Encryption is forbidden.
- Use of standards-based metadata is mandated.
- External content references are forbidden.
- LZW and JPEG2000 image compressions are forbidden in PDF/A-1, but JPEG 2000 compression is allowed in PDF/A-2.
- Transparent objects and layers (Optional Content Groups) are forbidden in PDF/A-1, but they are supported in PDF/A-2.
- Provisions for digital signatures in accordance with the PAdES (PDF Advanced Electronic Signatures) standard are supported in PDF/A-2.
- Embedded files are forbidden in PDF/A-1, but PDF/A-2 offers the possibility to embed PDF/A files, allowing archiving of sets of PDF/A documents in a single file. PDF/A-3 allows embedding of any file format such as XML, CAD and others into PDF/A as complete archived objects.
Read more about this topic: PDF/A
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