Cannot search a document

Do you know how the document was created?

When the PDF is open use the key combination <Ctrl> + D to bring up the PDF's properties. and select the "Description" tab.

When you use the "Text Select" tool are words highlighted an area of the PDF is a larger section of the PDF selected?

If an area is selected the PDF or section is an image of text and not actual text. The PDF will need to be processed by an Optical Character Recognition program like the paid for Acrobat. Acrobat DC can scan PDF that are combinations of text and scanned images of text.

Reformatting your system should be a very last step and is very rarely done to correct an application issue.

Uninstall and reinstall the app

I hope your problem is solved

Or otherwise format for system

The fact that you see it on the page doesn't mean it's actually there as real text. It could be a part of an image, or it could be text but with an incorrect encoding.
Are you able to select that word with the Text Selection tool? If so, what happens when you copy it and then paste in another application (like Word)?