Okular used to have a "Save copy as" option (e.g. in Kubuntu 2016.4 LTS).
It is MIA now. I see some bugs referencing this (e.g #348644), but did not find an explicit bug describing its removal.
I used this all the time. Because web browser rendering of PDFs is still somewhat janky, I always set up firefox to use okular to open all PDFs. Then I want to save them. Unfortunately, the "Save as" dialog always defaults to the mozilla temp directory (where the original file is). The "Save copy as" dialog used to default to the last directory where you actually saved a copy, so when you are saving multiple PDFs to a directory, it was much more functional to do it this way.
This is a removal of a very useful feature, so it feels very much like a regression.
Save as is just Save copy as, isn't it?
"Save as" defaults to the directory containing the original PDF.
"Save copy as" defaulted to the directory where the last "save as copy" was performed.
So when Mozilla opens PDFs by passing them to okular, the "Save as" directory will always be somewhere under /tmp.
BTW, the "Save copy as" directory was (very nicely IMO) maintained across logouts, reboots, etc.
"Save Copy As" is not really a standard thing and it wouldn't be obvious what the difference between it and the standard "Save As" feature is. I think it might make more sense to have the "Save As" action remember the last-used save directory, as many other apps do. We've had various other requests for this. Marking as a duplicate of those, since implementing that feature would resolve this issue.
*** This bug has been marked as a duplicate of bug 400103 ***