| Description |
The Portable Document Format/ Archive is a format designed for long term preservation by Adobe Systems. PDF/A is a simplified version of PDF 1.4, with all of the features from PDF 1.4 that would impede long term preservation removed. Removed features include Javascript, Audio/Visual content, LZW compression and encryption. A major principle of PDF/A is that it is self contained and not reliant on externalities thus all font and colour information is encoded into the file. PDF/A files are larger than other types of PDF files due to the need for embedded information.
PDF/A supports two levels of compliance PDF/A1-a (Accessible) and PDF/A1-b (Basic). PDF/A1-a is fully ISO 19005-1:2005 (PDF/A-1) compliant whereas PDF/A1-b is less stringent and not compliant. PDF/A1-a requires tagged PDF and Unicode whereas PDF/A1-b does not.
The signature identification proposed for PDF/A 1b has been tested against a number of PDF/A and PDF files for verification. However, PDF itself is a complex format, and while the PDF/A 1b signature contained in PRONOM will identify many PDF/A 1b files, DROID can only identify what a file asserts itself to be. As there are a number of ways in which PDF/A 1b files can violate the PDF/A 1b conformance, which can not be spotted until the file is parsed, it is recommended that PDF files are tested against validation software when attempting to confirm identification. Further information concerning PDF/A violations, and a test suite of PDF items which fail to conform to PDF/A standards, can be found at http://www.pdfa.org/2011/08/isartor-test-suite/ |
Details: File format summary
: detailed report on file format 
Digital Preservation Department / The National Archives
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