Can I get this document back

C:\Users\latha\AppData\Local\Packages\Microsoft.MicrosoftEdge_8wekyb3d8bbwe\TempState\Downloads\J&J Fireplace replacement letter.odt does not exist. I have saved other documents and can open them. I am not sure what I did wrong with this document.

If a file is reported to not exist it’s most likely it doesn’t exist - in the given location with the given name. It may have been moved or renamed. Did you already check the pathname using your file manager (Win Explorer)?
By the way: The pathname is uselessly bloated.

The pathname isn’t just bloated: it’s that user made a great mistake using a temporary file (i.e., had been asked to save a downloaded file or to open it (from a temporary storage); answered “Open” → meaning “it may be dismissed after I look at it”; worked with the file and saved some changes; and was surprised that the file had vanished later).

In Windows Explorer, top right if in windows 10, there is a search window, as there is in all file managers, somewhere, they can search in a folder or the whole disk. By using the wildcard * in all file managers, you could put in Firepla*.* which will search for all files starting with Firepla, they will show up, and will let open it, and will also show you the path to them. Good Luck.