PDFs can be edited but only with searchable text. If you design and build a PDF then its probably already set up for searchable text. You can then edit or copy any of the data (if not locked by the creator). If you do scans of documents or older PDF versions, then youd have to convert it to searchable text first, then you can do what you want with it. Building and converting pdfs needs special software (Acrobat Pro) and some word editors have the feature. You can design say a Word or Pages document and then export to PDF. You dont quite have all the features of Acrobat Pro, but it has a lot of useful ones that a basic user would use most often.
I build PDFs all the time for personal use in Pages.