I have tried this with files produced on a MAC using pages, on a windows PC using Adobe formatted pdf files. Using DirectFTP, the error occurs very often but not always. I uninstalled DirectFTP and reinstalled....no change. As I suggest, this has occurred only recently and since I have installed the latest creators update I suspect something has changed inside windows to create the issue.
Anyone else with similar issues? Solutions? by the way, html files css files etc all upload correctly it is only pdf files.