I believe that you must publish drag drop data in the format that they
expect. You should drag and drop from explorer to your application and
then enumerate all of the Data types in there. Thre should be 1 or 2
data formats that should jump out. Then enumerate the data and see what
format. Then merely try publishing that when you begin a drag and drop
operation and see if the application accepts. This should work with any
local files that you are transferring, any remote files would have to
be downloaded to the client and then you would send the temp file paths
to explorer or whatever target application.

Hope this helps