The essentials
With local processing, your browser opens the selected file, applies JavaScript operations in memory and downloads the result. That avoids the need to store document contents on a conversion server, but does not protect an already compromised computer or unsafe browser extension.
Practical steps
Some operations download an open-source processing library from a content distribution network. Downloading a code library is not the same as uploading your PDF contents. You can inspect network activity in your browser developer tools.
What to double-check
For highly sensitive files, use a trusted device, verify the address and inspect the final document—including metadata—before sharing it.
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