PDFs are available in different versions and used for different purposes; not every PDF is suitable for long-term preservation.

• Versions: PDFs were first introduced in 1993 in Version 1.0. Version 2.0 was released in 2017.
• Range of applications: Different PDF subsets are used for different purposes. The standards can be combined with each other.
  • PDF/X and VT: Used in the printing industry
  • PDF/A: Electronic archiving
  • PDF/E: Technical documents/engineering
  • PDF/H: Health care
  • PDF/UA: Accessibility
• PDF/A: Generally used for archiving. PDF/A consists of the following subcategories:
  • PDF/A-1: Suitable for long-term preservation. Recommended for all documents without images. Based on PDF 1.4.
  • PDF/A-2: Suitable for long-term preservation. Recommended for all texts with or without images. Based on PDF 1.7.
  • PDF/A-3: Allows embedding of arbitrary additional files. However, standard long-term preservation is not guaranteed.
  • PDF/A-4: based on PDF 2.0. Use this version only if absolutely necessary and if so choose conformance level "e" (not: "f"). Please contact us for further guidance.
• PDF/A Levels:
  • b: Identical representation. Generally used for scanned documents or images. It's best to use PDF/A-2b in this case.
  • u: For scanned texts with OCR.
  • a: Additional access to the content itself. Guaranteed access to the file as text. Enables accessibility. E.g.: PDF/A-2a
• Conversion: PDFs that do not comply with the PDF/A standard can often (but not always) be converted into PDF/A using the right software. The ZHB uses veraPDF to validate PDFs.
• We recommend PDF/A-2a as the best file format for all texts produced digitally. For simple scans of images, etc., we recommend PDF/A-2b.