How to unredact a PDF(and test your own files)
Unredacting a PDF means recovering whatever was hidden under a redaction. Whether you can depends entirely on how it was done. If the text was only covered with a black box, it's often trivial. If the text was actually removed, you can't get it back, because it isn't there anymore.
There's a good reason to try this on purpose: checking whether your own "redacted" file is actually safe before you send it.
How black-box redactions get reversed
Copy and paste is the usual route. Select the page, paste it into a text editor, and the hidden text often comes straight out from under the box. Sometimes it's even simpler: in many editors you can click the black rectangle and delete it, and there's the text. And don't forget the document metadata, comments, and form fields, which a box never touches.
Testing your own PDF
Open the finished file, select all the text, copy it, and paste into a plain editor. If anything you meant to hide shows up, your file can be unredacted and isn't safe to share. Check the document properties too. The longer version.
Redacting so it can't be undone
Use a tool that physically removes the text, images, and shapes inside each box and strips the metadata, instead of drawing over them. Once the data is deleted, there's nothing left to unredact. Ours does exactly that in your browser, with no upload.