We use libreoffice to generate pdf-figures from odg files (automatically via makefile) and include these in documentation generated by sphinx that via LaTeX ultimately produces a pdf file. This works nicely. However, starting with libreoffice 7, libreoffice generates pdfs with version 1.6. And pdflatex as used by sphinx (4.1.2) only accepts PDFs up to 1.5. producing warning messages such as
PDF inclusion: found PDF version <1.6>, but at most version <1.5> allowed
That would easily be fixable by including \pdfminorversion=6 early in the generated LaTeX file. However, putting it (first) in the preamble via conf.py is too late
! pdfTeX error (setup): PDF version cannot be changed after data is written to the PDF file.
Are there any other legal means to just insert raw LaTeX early (without resorting to scripted file manipulation)? Or do you have any other hints on how to specifiy the pdf version that gets produced by LaTeX/sphinx and thus get rid of the warnings. I know, just warnings, but these things tend to become errors sooner than one might think...
First of all, some of the answers to this question might be useful if you definitely want to upgrade to PDF version 1.6.
On the opposite, if the actual PDF version of your figures is not an issue, you can also manually force the PDF's to insert to be of version 1.5, using Ghostscript in the following command taken from here:
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.5 -o output.pdf input.pdf
That way, you make sure avoiding inserting any instability issue, messing up with LaTeX configuration. (even though setting up \pdfminorversion=6 should be fine by now)