In the event that a file has accidentally been deleted (within the last 30 days), you can easily self-recover it.
To get started, right-click anywhere in the open space in the folder, and select "Properties" from the menu that opens.
In the window that opens, click on the "Previous Versions" tab that appears at the top.
When you click on this tab, your computer will start to load all available snapshots. It may take several minutes for all of the snapshots to load.
Select a snapshot from a time when you remember the file being present, and double-click it. In this case, I remember the file was there when I came into work this morning, so I'll open the snapshot from 7am today.
This will open a new window, showing all the contents of the folder from today at 7am. Notice that the missing file is present here, and the address bar also shows that we're inside of a snapshot.
Since the file we want is here, simply click on the file in the snapshot window and drag it back into the normal folder. This will restore your file, so you can use it again.
After the file has been restored, close the snapshot window, and the properties window.
Now, your file has been restored, and you're all set to use it again!