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.