It's a bit of a pain, but you can store `~/.local/share/okular/docdata/` in version control or your favourite cloud storage provider, and then you'll get synchronised annotations.
When I say a bit of a pain, I mean it - I switched to Mendeley with great sadness because its mobile application means I can read and annotate papers on my tablet and have it synchronised perfectly with my desktop.
On a semi-related note: the Mendeley mobile application makes selecting text a joy on a touchscreen with a kind of magnifying glass. I really wish it was built into Android system wide.
You have to explicitly save the file after making the annotations. I've been doing this for years with Okular, indeed, Okular having out-of-file annotations is news to me :)
When I say a bit of a pain, I mean it - I switched to Mendeley with great sadness because its mobile application means I can read and annotate papers on my tablet and have it synchronised perfectly with my desktop.
On a semi-related note: the Mendeley mobile application makes selecting text a joy on a touchscreen with a kind of magnifying glass. I really wish it was built into Android system wide.