For some reason, the French government sometimes relies on weird PDF forms which can only be opened using Adobe Acrobat Reader and, for some reason, can't be exported to a "regular" flat PDF that Preview understands.

Here's what it looks like, using Preview

And trying to print it as a PDF, which requires a bit of effort, yields... that

Not quite the success I had hoped for.

There is, however, a way!

Solution

Which involves

• creating a fake network printer,
• 'printing' the documents with it, using Adobe Acrobat Reader
• finding the PostScript files that are generated by navigating to /private/var/spool/cups, which apparently requires sudo (so `sudo -s

sudo -s
cd /private/var/spool/cups

• identifying the proper PostScript files, most likely by timestamp:  ls -l
• converting them to PDF files using pstopdf (man pstopdf for more info. macOS really is full of many nice tools, starting with Preview, despite it's failings here).
• giving you the rights to read the generated PDF files: chgrp USERNAME GENERATED_PDF_NAME.pdf
• and finally moving it to somewhere more accessible: mv GENERATED_PDF_NAME.pdf ~/YOUR/PREFERRED/FOLDER/GENERATED_PDF_NAME.pdf

Yeah. That's a lot of steps and quite contorted for something that should be simple and straighforward. So, many, many thanks to user65535 for this great StackExchange answer. It definitely helped me a lot.