There are some fundamental tasks we need to do with most if not all documents. One of them is to compare two versions of what are essentially the same document. These might be legal agreements, or revisions of a report, which are quite likely now to come in PDF format. This article explores how you can compare the contents of two PDF files, or perhaps why you can’t.
Comparing PDFs isn’t a feature you’re likely to find in apps which otherwise have rich support for the document format. It’s more likely that they’ll offer some form of redaction but not the ability to make any comparison between two documents. Try Adobe Acrobat Reader, and the tool will be offered, but the only way to obtain it is to upgrade to the full Adobe Acrobat DC, on a monthly subscription. That’s an offer that most will wisely refuse.
A free solution is to export each of the documents in the form of text, and use a powerful text editor like BBEdit to compare those text documents. If you have Apple’s free Xcode SDK installed, you could use its FileMerge app, which is hidden away inside the app bundle and accessed through the Open Developer Tool command in the Xcode menu, but I prefer BBEdit’s Find Differences… command in its Search menu.