While in Ubuntu 16.04 this was the default and it was very convenient (at least for me), in Ubuntu 18.04 it always goes to "~/Documents" forcing to navigate to the chosen folder every time.
The use case is probably common: browsing the web reading pdf documents, one may want to keep some of them organized. The probability of several documents browsed in the same session going to the same folder is much higher than not.
This question "...make nautilus to automatically suggest the folder 'Documents'..." ask for the opposite in previous Ubuntu versions, but the solution requires changing the source code, recompiling evince and stop receiving updates for it. In another old question "Can I stop apps from selecting “Recently Used”...", file selector setup is mentioned but the options are outdated.
Is there a setting to control "Save as" behavior in evince or all programs?
It seems that the only solution to this problem is a modified source and recompiled application. I have created a version with an additional command line parameter (--documents-dir) that enables the user to specify the default save as directory. For details, see this post.
I have also created binary packages for 20.04, which are available from my PPA:
Use Xreader. It's one of the Xapps provided by the Linux Mint Team and a fork of Evince. It opens the same folder you saved your last document.
Forgot to mention: You can use i.e. this PPA to install: https://launchpad.net/~embrosyn/+archive/ubuntu/xapps
Maybe not exactly what you want, but the default save folder can be changed from
~/Documents
to whatever you prefer by changing the variableXDG_DOCUMENTS_DIR
in~/.config/user-dirs.dirs
. This can be done, e.g., by(Tested with Fedora, I hope it also works in Ubuntu.)