As @Alan-Kilborn said, once you closed the unnamed tab, Notepad++ deleted the session periodic-backup file, and thus “your data is gone”.
But assuming you had the session-periodic-backup turned on (it is turned on by default), then at one point, Notepad++ was saving copies into the %AppData%\Notepad++\backup\ , as @Terry-R described. So the files were written there at one time, and then deleted. That means, if you are lucky, an application like Recuva might be able to find and undelete the recent periodic backup for you. But with the amount of time elapsed, it’s getting less and less likely. Sorry.
In the future, if you want to cut from FILE1 to paste into FILE2, a better sequence would be:
save FILE1I understand you might not have a named file for FILE1… but if this is data that is critical enough to you that you are desperate to recover it, then it should be critical enough to use up some disk space while you are in the middle of manipulating it. cut from FILE1 paste into FILE2 make sure FILE2 looks like you expect save FILE2 go back and save the empty FILE1 close the empty FILE1 use Windows Explorer or other filesystem tool to delete the empty FILE1
…That way, any time before step 6, you can go into FILE1’s tab and UNDO to get back the original file.
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FAQ: Periodic Backup vs AutoSave Plugin => Describes the builtin “Session Snapshot and Periodic Backup” feature and compares it to the AutoSave Plugin Recuva => completely unaffiliated with Notepad++ or the Notepad++ Community Forum; listed as an example of file recovery software for Windows with no guarantee or warranty, explicit or implied, by its listing in this post