Every tool here runs on your own device. Your files are never uploaded, there is no sign-up, and nothing is added to your file.
Most online tools send your file to a server, change it there, and send it back. That means your file sits on someone else's computer, at least for a while. These tools do the work inside your browser instead. The file is read from your phone, changed on your screen and saved back — it never travels anywhere. That also makes them fast, and they keep working on a slow connection.
There is no account, no watermark and no daily limit. The site is paid for by the adverts on the page, which is why the tools themselves can stay completely free for everyone.