how to restore a pdf file

In the Finder View menu, select Show Path Bar. Open a new Finder window, and in the Search area, type the following substituting the date range that you believe the PDF was on your Mac. This will find all of the PDF documents in your home directory hierarchy in that date (mm/dd/yyyy) range. You can substitute created, or modified for the date keyword below.

date:05/01/2016-06/01/2016 AND kind:PDF

Clicking on the found PDF will reveal that Finder Show Path Bar, and the location of the PDF.

Any chance that the PDF is on your iCloud Drive, or on another non-Apple cloud storage location?

There is also the possibility that the PDF was backed up by Time Machine, and retrievable via a Restore of that PDF.

Accidentally deleted, corrupted, cannot find it on your Mac? Be more descriptive of your particular problem. We are not mind readers.