[Zubersoft]

iOS locks down things pretty hard in terms of file storage. Each application has their own sandbox in which their files have to live. So MobileSheets will have its own storage that no other application can access, for example. So if you installed forScore, it would largely be the same situation - it will copy your PDFs into its sandbox and if you wanted to move them to MobileSheets, you'd have to export all of the files from forScore and then import them into MobileSheets. Using my macbook, I was able to select my tablet in Finder, then drag & drop a folder containings lots of PDFs on MobileSheets and it copied the files into the sandbox for MobileSheets so that MobileSheets could access them directly. 

Mike