Hello
In earlier versions of okular, PDF annotations were saved as some metadata, which made them pretty useless when sending the PDF files to someone else. Therefore I used PDF-Exchange-Viewer (under wine) to annotate PDFs, but this crashes recently very often. Looking desperately for another solution I have discovered that since 0.15 okular can save annotations directly into the PDF file. https://docs.kde.org/stable4/en/kdegrap ... tions.html
I have okular 0.23.2 so I gave it a try. I made a yellow highlight of some test and used File>SaveAs as suggested by a popup window. When opening the saved file in acroread9 or xpdf this highlighing was indeed visible. However, when opening the file in firefox or chromium-browser, the highlight created by okular was not visible, but other highlights (which I had made with PDF-Exchange-Viewer) were visible. Uploading the file to google drive, the highlight made in okular was not visible.
Can somebody give some explanation, why this is so, and if one can make PDF annotations in okular which are really portable?
Thank you
Daniel

Sounds more like a problem with Firefox or Chromium to me.

Testing with the recently released Okular 1.3 and Poppler 0.61 to create the annotations, Firefox changes the cursor on mouse over and displays the author (but fails to show the highlight), and Chromium works just fine nowadays.

IIRC, Firefox might have plans to switch to the same PDF engine Chromium is using (PDFium), this is called "Project Mortar". Currently Firefox uses "PDF.js", you could try whether this project has a bug about that or report a new bug to them.