A possible factor here is that recent versions of Word, Excel etc. don't use
standard shortcuts. (Why I'm not sure, but they use some special kind of
shortcut that's not found anywhere else)

You can try creating a standard shorcut to winword.exe etc. in the Progam
Files folder, and see if that works. In principle it should, as all dropping
a file does is to execute "program.exe %1" where %1 is the file's full
pathname.