PDF/A Validation

The primary purpose of PDF, which is why it is so popular, is to be opened and viewed on all systems and devices while keeping its layout. Since 1995, millions (billions?) of users generate and convert their files to PDF to archive them electronically. However, in 2005, a new PDF substandard specifically developed for long-term archiving was released. So why wasn’t PDF sufficient for this need?
If “regular” PDF is perfect for day-to-day use, its specification allows actions that can hinder future viewing and prevent a flawless archiving of files. For instance, locking a document with a password goes against the idea of accessing files. Another issue is the use of dynamic content like launch, sound, and movies, as they require the use of third-party applications that may not be available in the future. On the contrary to PDF, PDF/A requires that all the information needed to provide a precise rendering of the document is contained in the file, including fonts, color profiles, images, to name a few.

PDF/A-1 is standardized under ISO 19005-1: 2005. Based on version 1.4 of the PDF specification, it lacks important functionalities such as JPEG2000 support, transparency, layers, and attachments.
The next version, PDF/A-2 (ISO 19005-2: 2011), is based on PDF 1.7 and includes what was missing before in PDF/A-1. An additional significant feature is embedding PDF/A files to facilitate archiving sets of documents in a single file.
PDF/A-3 (ISO 19005-3: 2012) is also based on PDF 1.7. The main difference is that it allows embedding arbitrary file formats (such as XML, CSV, CAD, word-processing documents, spreadsheet documents, and others) into PDF/A documents.
Finally, in 2020 PDF/A-4 (ISO 19005-4: 2020) was released to match the global improvements brought by PDF 2.0

In addition to versions, the PDF/A specification includes several levels, each for different purposes.
Level a (with a for “accessible”) is found in PDF/A-1, PDF/A-2, and PDF/A-3. It aims to increase the accessibility of the file thanks to a logical document structure and necessary tags and information to help users with assistive technologies.
Level b (with b for “basic”) is found in PDF/A-1, PDF/A-2, and PDF/A-3. It only includes the necessary features needed for reliable reproduction of the document’s visual appearance.
Level u (with u for “Unicode”) is found in PDF/A-2 and PDF/A-3. It requires all text in the document to have Unicode mapping.
With the release of PDF/A-4, based on PDF 2.0 specification, a new f-level replaces the a, b, and u levels. Furthermore, PDF/A-4f allows files in any format to be embedded.
Level e is also new and specific to PDF/A-4. It replaces the lesser-known and used PDF/E-1 (ISO 24517-1: 2008, Engineering document format using PDF standard) based on PDF 1.6. In addition, PDF/A-4e includes RichMedia annotations for 3D content in U3D or PRC format and embedded files.