Strange, extra lines in images in .pdf saved with MS Word (happens with images from R and possibly other images)

i had this problem, too. it resulted from using the Track Changes feature in the word doc. the lines showed up in the PDF even though the word doc was set to show no changes. You can fix it by going to the Review Menu, click the drop down for Show Markup, and uncheck all of the items (comments, ink, etc.). When I converted again, the lines were gone.