Is there An Android App That Syncs Not Only PDFs But Also their?

Is there an Android app that syncs not only pdfs but also their annotations with the files on your Desktop?

Not to my knowledge, and that’s because it’s really straight forwards to do it manually. The easiest way is to put all music on your desktop into a single folder. Using your charging cable, connect your android to your desktop via the charging cable, and then unlock your phone. You should be able to navigate to a set of folders that look similar to this. I have a few extra ones because of some apps, and these may change depending on your specific android device. From there, copy any MP3 files you want to have on your phone to the music folder shown there. Once copied, you can unplug your phone, and all MP3 files that were transferred can be played in the music app.