PDF is what I call a "final file format", it does not lend itself to major edits in a document. The editing tools have improved over the years, but are still very limited compared to what you can do in e.g. MS Word. The best way to make big changes (and removing a line is a big change), is to go back to the original document, make the change there and then export the document to PDF again.
If that is not possible, you may be able to convert your document to Word (File>Save as Other>MS Word), make your changes and then convert to PDF again.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com