If you're exporting a PDF/A from Word for a court filing, tender submission, or any EU public administration that requires long-term archival format, worth knowing: since Word 2019, the native "Save as → PDF/A compliant" option defaults to PDF/A-3, not PDF/A-1 like older Word versions did. This has been reported repeatedly on Microsoft's own support forums.
The problem: a lot of legal and government archiving systems specifically require PDF/A-1 or PDF/A-2 and will reject PDF/A-3 outright — it's a newer, more permissive standard (it allows embedding arbitrary files inside the PDF, which is exactly why some archival systems don't trust it for long-term preservation).
There's no built-in way in Word's UI to force PDF/A-1 output — you either need a third-party converter, or you validate/downgrade afterward with a tool like veraPDF (free, open-source validator, good way to actually check what conformance level you ended up with — don't just trust Word's "PDF/A compliant" checkbox).
Side note since I make one of these tools: I'm the developer of Edito PDF Conversion, which handles exactly this — converts to PDF/A-1B/2B/2U/2A/4/4F specifically, running fully local (no cloud/telemetry). Not trying to just plug it — mainly wanted to flag the Word default behavior since I see people get burned by it, but happy to answer questions if anyone's dealing with this.