Thanks for the reply, Gary. The form was originally in LiveCycle. It was then converted into an Adobe DC document. I am copying and pasting cells within the document, and when I copy and paste sometimes bold lines form. Someone told me that I could open the document and LiveCycle and fix the issue; however, when I attempt to open the document in LiveCycle I have conversion problems and the document does not appear as it should.
Do you know the origin of these documents? How they were made and/or anything else about them?
When you go into Edit, are you able to select these lines? What I have a hunch is that the lines are not "in addition" to the normal thin lines you are expecting so that if you were to delete them, there would no no line. Nonetheless, you can try and and hopefully my concern may not be correct.
One other option is if you have Adobe Illustrator, you can open these documents into Illustrator, select the lines and make the lines narrower. Unfortunately there's no way I know of to change the thickness of a line in Acrobat.
If you can get to the origin application of the document, than you can chose thinner lines at that point.