why are my pdf files unreadable

When I open a pdf file all the formatting is gone. The text and pictures run together etc… Is there a way of fixing this?

Possibly because LibreOffice is not a PDF reader. See Adobe Acrobat Reader DC Download | Free PDF viewer for Windows, Mac OS, Android

But no one has to use Adobe. You can also use Sumatra https://www.sumatrapdfreader.org/free-pdf-reader.html And there are others as well. I think most browsers also include a PDF reader.