More on ScanTango and Redacting PDFs

More on ScanTango and Redacting PDFs

After my post about redacting PDFs without Adobe, Craig Landrum, the author of ScanTango sent me an excellent email. With his permission, I am posting his comments for your benefit.

I’m the author of ScanTango and I really appreciate the nice mention of the application in your blog. Some feedback on redaction:

When most applications redact, they simply put an opaque white or (more typically) black rectangle over the sensitive areas of the document. In most PDF software what this actually does is simply creates an opaque rectangular image object that sits above what is being redacted (whether that is portions of an image or actual selectable text). This allows “PDF hackers” to dig below the obscuring layer you just applied to get to the original stuff beneath. For this reason, ScanTango provides a “Convert to Bitmap” function. This function creates an bitmap image into which it draws the PDF page you convert, creating a pure, non-layered bitmap with everything on a single image plane. Because the layers are removed in this plane, PDF hackers have nothing they can dig into. The newly created bitmap plane replaces the original (perhaps text-based) page in the PDF document. This means that the text on that page will no longer be selectable.

Printing to a PDF via Apples print dialog may or may not do this type of conversion (I have not tested this). One way to check is to print a text-based PDF via Apple’s print dialog and see if the output PDF still contains selectable text. If it does, you haven’t hidden anything and are still vulnerable.

ScanTango takes the brute force method to solve this problem as I described above, assuring you that what you intend to hide is really, really, hidden
In our latest version, we allow potential buyers to try the app with their own hardware. Until the application is registered, all pages that are scanned have a gentle registration reminder stamped on them. However, existing PDFs that you input and redact will not have this warning, so for people that just want to redact existing PDFs, it’s a free tool (a nice word to your legal friends above the app would be appreciated though).

Thanks, Craig! I definitely feel better about redacting live-text PDFs with ScanTango after you explained what’s up.