Okular 1.8.2 says the document contains XFA forms and it's not yet supported. This is the first time I ever even heard of this. <https://enwp.org/XFA> says the technology is already deprecated.
I have used Okular many times for PDFs with embedded forms (no apparent special name). I think you should notify the originator of the unusable PDFs that they should redo the file with regular embedded forms so that they work in most PDF readers.
In my experience these are PDFs that embed JavaScript. I don't think there is much of an appetite for building yet another JS interpreter into the desktop...
Please post any examples of those to the evince project as a bug report.