PDF is explicitly designed as a final output format (and PDF/A is explicitly designed for archival purposes). They're good for that purpose, but it's literally

PDF is explicitly designed as a final output format (and PDF/A is explicitly designed for archival purposes). They're good for that purpose, but it's literally like storing the digital version of a printed copy of a document rather than the source. That's fine if your only goal is preservation for reading, but preservation in a format that can be edited, converted, transformed, etc., lets out PDF as a target.