PhilterPaper commented Dec 18
Even simple PDF files produced by PDF::Builder fail validation tests such as
http://www.pdf-online.com's. Unfortunately, the error messages are rather vague ("incorrect meta data" and "not PDF 1.4 compliant", etc.) and not much use in seeing what's missing or wrong. Does anyone know of a good validator that gives useful information? Then I can see what needs to be added or changed (such as inserting a default media size entry). Are there any flags or settings on Acrobat Reader to output good diagnostics? Apparently, it tries to fix up a PDF file when it reads it in. Does the PDF 1.7 spec clearly spell out anywhere what's needed? I seem to recall seeing some "mandatory" or "required" information here and there, but it's scattered.
pdf-online also claims to check PDF/A compliance (see #52 and #76), but we really need to get the PDF standards compliance fixed first, before tackling PDF/A.
Note that pdf-online, and possibly other validators, take your PDF file to their server. Watch out that you don't have any sensitive information in your PDF that you are testing!
With regards to PDF validation, this might be used in testing PDF::Builder code, as well as example programs. At a minimum, we need validation that what the library is putting out is a clean PDF. The main burden of making sure nothing is
missing (e.g., media size) may still fall upon the user of the PDF::Builder library, but at least the library could help out a bit more than it does.