We open the PDF files via Sharepoint, then a file is opened online via the Adobe Cloud PFD Viewer.
These can then be edited and saved there.
Now we come to the problem.
If you edit a PDF file and edit it with the couser (mouse) it works and there is no problem.
But if you edit the file with your finger or the pen and write things into it, the written thing disappears a short time afterwards. But only if you put the pen down and then write something new, the previous one disappears.
The funny thing is that if you save the file and then open it again, everything that has been written is there.
So it can be summarized that if you make an input with the pen or your finger (touchpad on the Surface), it disappears immediately but is there again when you open it again.
If you paint directly with the mouse, this doesn't happen.