I tried some coding myself and succeeded in adding a KLineEdit to set the subject of a single annotation and for annotation tools. However, I was not able until now to get the information for the annotations saved (it works for the tools only). As soon as you save the file the subject information gets lost and is reset to its prior value. I would very much appreciate some hint how this could be done. You can have a look at my tinkering here: https://github.com/Freedrich/okular The subject entry of markup annotations doesn't seem do be wildly used. My objective is to have this information gathered be another program in order to show you every annotation with a specified subject across documents. In my opinion this would significantly enhance the functionality of computer based document annotation. (In case you're interested: I made some slight changes to the Zotero Add-on Zotfile to make this possible. https://github.com/Freedrich/zotfile/tree/separateNotes)
Thanks for your work! Please feel free to submit any of it in patch form to phabricator.kde.org. We have good documentation: https://community.kde.org/Infrastructure/Phabricator Even if your patch is not complete, just add [RFC] ("request for comments") to the beginning of the title to solicit feedback.
Friedrich, any success with the link from comment #1?