Depending on exactly what you use it for, there are a number of Libre CAD packages out there. It's true none will match RentalCAD sophistication in many categories, they can cover many use cases and don't cost thousands a year to rent: FreeCAD, LibreCAD, BRLCAD, and a few others I can't think of right now.
I've also used QCAD with success in the past for standard 2D mechanical drawings, though it's not Free software, it is free to use.
@J - LibreOffice Draw can edit PDFs. I use it for filling in forms on PDFs not made with fillable fields.
@Jen - Neither of those two excellent tools allow editing fields or text. (I love PDF-Shuffler!)
@Lori - PDF was never meant to be parseable or editable. It's meant to be the human-readable end point after all that is done. It's purpose is to present a document the exact same way regardless of application, OS, or machine. It does that pretty well.
Depending on exactly what you use it for, there are a number of Libre CAD packages out there. It's true none will match RentalCAD sophistication in many categories, they can cover many use cases and don't cost thousands a year to rent: FreeCAD, LibreCAD, BRLCAD, and a few others I can't think of right now.
I've also used QCAD with success in the past for standard 2D mechanical drawings, though it's not Free software, it is free to use.