When you cannot find your edited files, try to look in these two places.
Scenario 1: You opened the original file by directly double clicking on the PDF file rather than opening it through PDF Reader app.
You can find your edited file from the "Recently Open" in PDF Reader app.
We strongly recommend you open PDF files through PDF Reader app to prevent missing your edits.
Scenario 2: The app closes during your editing. When you reopen the app, the file is not in the "Recently Open" list.
You can find this copied file from the following path:
(The [UserName] is the user name you use on your Windows device.)
When you find the file, add .pdf as its extension. Then it will be a usable PDF file.