John Levine writes:
Among valid PDFs, do you include PDFs that are coded to prohibit text
extraction? How about PDFs that are just bitmap scans of printed
documents, like the PDF versions of some early RFCs from the 1970s?
Use the most conservative (and thus probably the earliest) version of
PDF. Later versions are designed mostly to make money for Adobe, and
they are scarcely needed for documents that contain only formatted
text and diagrams. Using an early version of PDF also guarantees that
the document can be opened with (almost?) any version of Acrobat
Reader or other software.
I still use Acrobat 4.x, and I have it set to generate Acrobat 3.x
documents, and I've yet to generate any document that requires a more
recent version of the software. If you limit yourself to the text and
simple artwork that has sufficed for the printed page for the past few
centuries, you don't need anything more recent, and you shouldn't be
using anything more recent.
Be conservative in what you require, and liberal in what you accept.
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