Question about a file in two places... or not.

I've always assumed that any Windows file can be in two folder locations at the same time using the same file name, but I just noticed something strange and wonder what's going on.

If I send an email message using my Windows Live Mail client and attached a PDF file, the original .pdf is still in its normal folder location; that is, what's attached to the email is essentially a copy of the original .pdf. I can send the mail and all is well, the original remains in its proper folder. BUT if I attach the .pdf and then slide it out of the mail program onto the Desktop, the original disappears. Luckily it was there on the Desktop and I simply put it back in the folder, but why would attaching it to the mail, and then removing it to another location (Desktop) remove the original from its normal location?

Yes, a single document can exist in 2 or more different Folders. It's just that 2 files of the exact same name can't exist in the same Folder. That has existed for a number of years.

If a program uses a file and that file gets deleted or moved there will be a problem in future use.

As for the "sliding out", the Desktop is a Folder itself, any transfer of a file from a Folder on an HDD to another Folder moves it whereas such a transfer between 2 HDDs or 2 partitions only copies it. The right-click drag of a file gives such choices. Note: in this instance HDD could be any type drive, just simpler to type.

The "copy" in the E-Mail was most likely just a marker or shortcut to the actual file, the action moved the file from one Folder to another one. It can be proved if having a second E-Mail address and replicating what you did.

The only thing I can add is that most programs don't have their own file management application, use File Explorer [and Windows Explorer of older versions] for their storage of documents.