A PDF file is not designed for editing.
Apparently there are two versions of the extension. Are you sure you got the right one?
Even if you did, I note that the 4.x compatibility ratio (as submitted by users) is 43% YES to 57% NO.
That means that most of the users that have submitted ratings believe that it should not be considered compatible with Open Office 4.x
I also noted that the author states
Best results with 100% layout accuracy can be achieved with the "PDF/ODF hybrid file" format, which this extension also enables. A hybrid PDF/ODF file is a PDF file that contains an embedded ODF source file. Hybrid PDF/ODF files will be opened in OpenOffice.org as an ODF file without any layout changes.
It sounds like your PDF is being recognized as a collage of pictures, rather than as an editable document.
Where did the PDF come from? If it was someone you know, ask them for a version that is not in PDF format, preference given to a file in Open Document format (.odt for Writer).
OpenOffice 4.1.7, LibreOffice 7.0.1.2 on Windows 7 Pro, Ultimate & Windows 10 Home (2004)
If you believe your problem has been resolved, please go to your first post in this topic, click the Edit button and add [Solved] to the beginning of the Subject line.