Conversion to PDF/A

ISO standard PDF/A-1 was published in 2005. The goal was to narrow down of the functional scope of PDF, so that standard-compliant files can be archived over the long-term. PDF was then still defined by the Adobe reference. PDF/A should, however, not create a new PDF reference. Instead, the existing PDF reference has been “scaled down”.

The second part of the standard, PDF/A-2, was published in 2011. The most important innovation was certainly the fact that this standard part could now be based on PDF as an ISO standard, ISO 32000-1 (corresponds to PDF 1.7). Also, the implicitly valid XMP definition of Adobe had, in the meantime, become the ISO standard.

As a result of the further development of the PDF format, new functions for PDF/A were also approved. Some examples are OpenType fonts, JPEG2000 image compression, and newer comment types.

The third part of the standard, PDF/A-3, was published in 2013. The only new feature is the option to embed any file. It is only necessary to identify the relationship between the embedded files for the PDF/A-3 enclosure: a previous version or other representation.

• Fonts: The best-known feature in this context is the embedding of the utilized fonts. Each font used must also be embedded. To reach the highest-level, Level a, you must also identify each character with the corresponding Unicode name, even if no Unicode font is used.
• Colors: Even colors should not be left to chance or the will of the printer. There are general color models – that have nothing to do with PDF. These should be used. And if that does not work, then the PDF file should be provided with the device it should preferably be output with. Then, a conversion to a general color model can be made later.
• Encryption: PDF/A generally does not allow encryption. Also, unlike a normal PDF, compression is not allowed. Images may be compressed using a standardized method – such as TIFF, JPEG and PDF/A-2 – as well as JPEG2000. More is not possible because the content of a PDF/A file should be accessed as simply as possible. The protection of the file against uncontrolled modification must be carried out by a management system (DMS). When a document is distributed, it is also possible to use digital rights management (DRM). Since this encrypts the files, a standard PDF/A must still be kept internally in stock.
• Digital signatures: Digital signatures can be used to prove that a PDF file has not been changed from a certain point in time. PDF/A-1 did not make any statements on digital signatures. It allowed them automatically. And because PDF makes manageable embedded signatures possible, this function can also be used. But only PDF/A-2 contains the reference to signature standards, so that errors in the use of signatures for long-term archiving are impossible.
• Transparencies: In the original PDF reference, transparency was described inaccurately. In the PDF ISO standard, they are now so precise that they can also be safely used in long-term PDFs. From PDF/A-2 transparency is allowed. This is the reason why there is no need to worry about PDF/A generation anymore. The ability to use transparencies is an important reason to switch to PDF/A-2 if you have previously created PDF/A-1s.
• Scaling options: PDF/A-1 had a size limit of 200 inches = 5.08m based on PDF 1.4. This was too small for many applications. Scaling in PDF/A generation was the work-around. In the PDF/A file itself, however, the original size was no longer known. With PDF/A-2, a standard scaling factor may now be used, the user units. This means that extensions of around 300 km are now possible.
• Levels: Previously in PDF/A, the usability of layers in the PDF was often missed. This PDF function is now also better standardized: a level must be marked as the default level. Then, levels may be used. An example is when converting from CAD models.
• Embedding files: A major innovation in PDF/A-2 was the ability to embed other files. If these files themselves are PDF/A compliant, this feature can be used. With PDF/A-3 you may embed any files. PDF/A-3 does not in any way guarantee the quality of the embedded files. To do this, rules must be imposed on them, in order not to avoid uncontrolled wild growth. However, there are numerous applications for the option of packing any files in PDF/A-3:
• 2-D PDF views of a design with embedded original 3-D geometry
• Invoice as PDF and stored invoice data as XML (ZUGFeRD – Central User Guide of the Electronic Invoice Forum, Germany)
• Originally non-PDF/A file but with a valid digital signature embedded in the resulting PDF/A file
• Marked files: Adobe has also created its own standard, the XMP standard, to mark files using XML tags. A file marked in this way carries the information for what it serves in itself; protection for the failure of the DMS system. XMP also includes several schemas for keywords. What if the keywords that you would like to use for your PDF/A archive are not included? Then, create your own schema then embed it into the PDF/A file.

PDF/A-1 is available with Levels a and b. From PDF/A-2, there is also Level u.

Level b is the lowest but guarantees the unique visual reproducibility of the PDF. This level is usually sufficient. Frequently, no higher level can be achieved with the available sources.

Level u also requires that all characters in the file additionally have their own Unicode name. Note: If you need a Unicode, you can achieve this with Level b. You just need to use a Unicode font.

Level a is the complete norm. With Level a, objects for automatic searchability can be marked, such as headings, pictures, indices. The first step towards PDF/UA is made here with Level a.