Right, editing PDF online with a Mac is safe--if you do it on a trusted site. Such websites as Smallpdf or Adobe Acrobat Online are associated with secure connections. Nevertheless, never share sensitive/private files. When you lack confidence, use the tools that are built in, such as Preview. When learning how to edit a PDF on Mac, start with offline tools first. Once you’re confident, you can try online options to expand your options for editing PDFs on Mac.