I'm looking for a program with which I can annotate PDF files with text such that this text is always directly visible.
Okular works fine for underlining, highlighting, etc. But when using Okular to make a text annotation, it disappears in a popup window.
I want to make text annotations that always show, without having to click on some popup windows.
Is this possible under Ubuntu?
If you would like to use true (editable) PDF annotations, then I guess you will have to live with how your PDF viewer (Okular, Evince, Adobe Reader, …) displays those annotations.
However, if you are ok with annotations which are ‘baked into’ the PDF (by actually editing the PDF and not just adding removable/editable PDF annotations) then you may want to have a look at PDF editing software like Xournal. With Xournal you can add highlighting, text annotations, etc.
After installing Xournal, you go to “File” → “Annotate PDF” and open the PDF file to annotate. Make your annotations and then go to “File” → “Export to PDF” to save the result.
Note: I had to uncheck “Use XInput” in the “Options” menu for being able to annotate anything – YMMV.