mv * /incoming/out/processed/
I do not know what the purpose of
*.gpgmask, as you have not mentioned that in your post.
Though the above solution is not transactionally safe. If new files are added during download, it will move even those files, although they were not downloaded.
There's an example for transactionally safe upload, with use of PowerShell script and WinSCP .NET assembly.
You can base your solution on that: