OK, sorry, I'm clearly not making sense.
I have a pdf annotation app on my iPad. At regular intervals, I sync (the function is called 'sync' in the app) with Drop Box, so that the latest changes I've made to documents are backed up.
Several of my other apps also offer to sync with Drop Box. However, in those apps (e.g. for those with photos or notes), I would want them to 'sync' the pdf files. So I'm wondering what people do if they use dropbox for several apps at the same time.
Is that clearer?