Moved from Editing & Exporting PDFs since this has nothing to do with that topic …
You didn't indicate how the PDF file was created or who created it, but the diagnostic very clearly indicates that either the original font was defective or whatever software created the PDF file did so incorrectly in terms of placing information from the Titillium-Regular font into the PDF file.
Try recreating the PDF file. If that doesn't resolve the issue, try using a different font and if that fixes the problem, it is likely a problem with the original font. If that doesn't fix the problem, most likely there is a problem with the software that is creating the PDF file.