Editing a PDF

I am trying to remove unwanted parts of a PDF, such as adverts (PDF created from web pages), but when removing the unwanted bits, the the formatting of the PDF is all screwed up, not by removing the graphics but by LibreOffice Draw. Is there a better program I can use which will not alter the formatting of the PDF?

Have you tried Master PDF Editor ?

I’ve installed it but not yet explored all it’s features.