“But I cannot find to open. How to find?”
Use Find Files/folders tool.

“How do I tell if If I have ext3?”
Use GParted or some other partition editor to view your disk.

“Can I limit a search …….”
Find FIles/Folders tool has options for the file type (.PDF), date range (before 1/3/2020) and where to search (Documents).
However, I would suggest that you search your entire /home directory. Inadvertently you could have copied those files to any directory.

@Charles

Open a terminal window and try to type a few characters of the command then press [Tab]:

$ ext3[Tab completion]

Follow the instructions in the guide to restore lost files.

Have installed ext3grep from Software Manager, and it says installed. But I cannot find to open. How to find?

How do I tell if If I have ext3?

Can I limit a search (when I get it working) to look for only .pdf after a certain date says Jan 3, 2020? Can I tell it to look at subfolders in ‘Documents‘ directory?

Note: the pdf’s I am looking for were downloaded into ‘Downloads‘ directory and then cut/copy to a Documents subfolder, and then alas deleted in error!

In another case it is best to turn off the computer and use Caine Linux that mounts the partitions in read-only mode and include: Photorec, Test disk and other tools.

As I stated in my post, for non-ext3 file systems, use Photorec