Border added when convert Word doc to Adobe PDF

Hello,

I am having trouble with unwanted/new borders appearing around some images when I convert a Word doc to Adobe PDF. I have Acrobat Pro and select "Save as Adobe PDF" to create the PDF. See image below for example of the thin gray lines that appear around some figures. However, when I instead print the Word doc to a PDF, this doesn't happen.

I have seen similar posts mentioning this problem, but none with a conclusive fix that I have found. I would appreciate any help in correcting this. Thank you!