I have discovered that photos can be deleted in pdf documents using free writer
Are there any additional pdf document editing features?
You can’t edit PDFs in the traditional sense with LibreOffice. LO sees PFDs as graphical documents and opens then in Draw, whatever you try to workaround that.
In Draw, a PDF is a collection of separate text boxes which means your editing capability is limited to the contents of the selected text box. If you shorten the text, nothing will be flown from the next one. If you add to the text such that you overflow the initial text box, either the text box expands (and eventually shadows adjacent text boxes) or the text is clipped to the size of the box.
Since the PDF is handled just the same as a Draw document, you can play with all the commands and features present in Draw to modify your PDF. Be aware, though, that this may damage the PDF structure and prevent correct rendition in PDF viewers.