For years, modifying a PDF meant either buying expensive software or uploading your file to a sketchy website. Today, modern web technologies have changed the game.
The Danger of Cloud Converters
When you upload a file to a cloud converter, you are literally giving them a copy of your document. You have to trust that they will delete it, that their servers are secure, and that they aren't reading your data to sell it.
The Power of Local Processing
Tools like PDF BOX use WebAssembly and JavaScript to process the PDF inside your browser. The file never leaves your computer. Your internet connection could drop out completely, and the tool would still work.