Latest: Leonard Rosenthol has since posted a followup on the discussion.

PDFSAGE wondered what the cons are with PDF/A compared to simple HTML for document archival. The debate generally comes down to what you think a document is. If it's an A4 page for printing, you probably want PDF. If a document is an arbitrary unit of information, I would suggest HTML.

Lets start why the PROS of PDF/A. You'll need Flash to view this PDF preview. Actually to do mostly anything with PDF, you need proprietary tools monopolised by Adobe.

You can't just assume people have a PDF viewer installed. Hence PDFSAGE shared his PDF document assuming I had Flash installed. Another proprietary tool. Great, what a start!

Cons of PDF/A

• The PDF viewer isn't nearly as pervasive as a Web browser. Is there a PDF viewer on your mobile? No, I thought not.
• The PDF viewer is slower than a Web browser.
• A PDF is many times larger than an HTML file. Imagine Wikipedia as a PDF/A file? That would be CRAZY.
• Since the viewer and content are much larger than HTML counterparts, PDF/A demands a faster internet connection. Have a slow connection? You're out of luck!
• PDF isn't part of the Web. It's non-trivial to get PDF content on the Web. People end up converting it into a PNG and that's a terrible loss of information.
• It's non-trivial to index and parse out information from a PDF
• "Protected PDFs" break common computing paradigms of copying&pasting
• It's non-trivial to edit content in a PDF. Indeed, PDFs are often designed to be static for archival and reproducible results. Though if information can't be maintained, one can argue it's dead.
• Only accurate representations of stored content can be produced if you embed the font. Bloat!
• A document is of little use unless it's transcribed into text. Scan a STASI file into a PDF. Great, now what? Storing it as a PNG would be even better as people would at least been able to view it easier.
• PDF has a poor accessibility record
• Non-trivial to diff, track and compare PDF documents
• An open standard? That you need to pay ISO 200GBP for?! Are there at least two interoperable implementations of PDF/A?
• Probably only one conforming implementation (Guess who!). Is there a test suite?

Pros of HTML

• You can read HTML in the simplest of text editors
• An algorithm for parsing HTML is openly defined
• You can "sign" an HTML file by using XML digital signatures. Widgets in fact use a subset called Widgets 1.0: Digital Signatures.
• Scalable. Want text on big or small? Sure thing.
• Easy to edit and maintain. Anyone can edit HTML with a plethora of tools and support.
• Simple to index, find and use the information marked up within an HTML file. Same is not true of a PDF.
• HTML is space efficient. PDF isn't.
• HTML can include "marginalia" like comments and notes.
• HTML has several ways of adding metadata support, though Google search generally does not rely on them for best results
• HTML can convey critical information. It's done so more effectively that PDF has ever done.
• Need to package some HTML content? (i.e. self-containment) Use a widget!
• You can generate static snapshots of HTML to formats like PDF, with tools like Prince. You can't do the reverse very easily!
• HTML is already the primary medium for archival of information! Checkout the waybackmachine
• Worried about data being tampered with? Mandate source control like git where each document can be explicitly tracked since HTML can be treated as plain text for this purpose.

Cons of HTML

• Can't be rendered consistently across devices or mediums -- HTML is not a (static A4 print) presentation format, it's a publishing format
• Printing is particularly tiresome, which is good news for trees
• HTML is living markup and it ideally needs to be maintained