If you don’t have Adobe Acrobat Pro, here’s a good alternative:
It’s an online tool; can also be downloaded
It shows the differences separately so you’d need to use something else if you need to combine the changes
I recompared the files from Draftable on PDF Converter Enterprise 7.2 to combine the differences on one file.
PDF Converter Enterprise 7.2 couldn’t match pages and contents so that was annoying. I had to do chapter by chapter with PDF Converter Enterprise, otherwise, it will compare the pages, which obviously would have different contents/chapter
There might be a way/option that I’m not aware of in PDF Converter Enterprise
PDF Converter Enterprise 7.2 is the one my uni is using to create/split/compare/merge/etc PDF