If I am not wrong you are using edit functionality of Acrobat. There you can select the edge or small bounding ox and delete it if it is not required.
If not please use Edit tool.
If you are facing any issue on any file please share the files.
An error occurred while saving the commentDiane Crook commented
i am having the same problem, now i am beginning to think the reason why is because the document I am trying to edit was a previously edited document