PDF/A (PDF/Archive) is a subset of the PDF format. It was designed specifically for the long-term storage of electronic documents. It was first proposed by the Association for Suppliers of Printing, Publishing and Conversion Technologies and the International Association for Information and Image Management. PDF/A is certified by ISO as International Standard ISO 19005-1:2005.
PDF/A has two key features. First, every document in this format should be completely self-contained. Therefore, it only uses fonts whose license allows for an unlimited number of views using all-purpose software with all such fonts being embedded in the file itself. Secondly, PDF/A documents may not use any outside data. Hence, they may not use hyperlinks. In addition, specifications for this format prohibit the use of audio or video clips, scripts, or commands invoking executables, encryption, etc.
ISO 19005-1:2005 defines two levels of compliance with the standard: PDF/A-1a and PDF/A-1b. The former provides reliable storage and reconstitution both of the appearance and the complete structure of an electronic document and defines that encoding must necessarily be Unicode. These files may be used for data searches and data extraction for processing. PDF/A-1b is less strict. It requires that an electronic document’s appearance only be stored and reconstituted.