Conformance levels apply to PDF/A documents only. A conformance level defines the quality requirements for the PDF document's content.
There are three conformance levels:
The conformance levels are incremental, meaning that the subsequent level includes the requirements of the previous level and other additional requirements. For example, all level U documents are also valid level B documents.
Each PDF/A document has a claimed conformance level. The Pdf Tools SDK validates this level by performing specific validation checks. For example, only PDF/A documents that claim to have Level U conformance (which can be either PDF/A-2 or PDF/A-3) are checked to determine whether they contain alternate descriptions of the content where needed.
Level B - Basic
Level B conformance determines the visual integrity of the document. It guarantees clear, long-term visual reproduction of static content in the PDF document. This is the default conformance level for all PDF/A conforming documents.
Level U - Unicode
Level U conformance guarantees the searchability of text within the PDF. Unicode text is copied to the output file, allowing it to be extracted later if required. This is for digitally created PDF/A documents and documents scanned using optical character recognition (OCR).
Level A - Accessibility
Level A determines the semantic correctness and structure of the PDF/A document. In other words, it preserves the document's logical structure and content text stream in natural reading order. It also ensures that conforming files can be accessed by devices used by physically impaired users such as screen readers.