PDFs that are opened externally get erased when saved to DTPO

I have a problem that happens not infrequently. When I open PDFs in Adobe Acrobat and annotate them and then save it. The original text of the file gets erased and only some of the lines of highlighting remain visible. Is this an issue with Adobe? or with having the same file open in two places by accident (maybe?) or is there something I can to make sure it doesn’t happen again?

Thanks@ Ben

Does the same thing happen if you annotate in Preview?

I usually use adobe, so I don’t know. But I can experiment. I should clarify, the file itself gets corrupted so it won’t work in either Adobe or DTPO or another PDF viewer.

Does this also happen if you open the same document via the Finder?

Haven’t tried that. But this definitely happens when i accidentally modify in both Adobe and DTPO

Under what conditions would this be happening?