Does redaction compress PDF files ?

[Tom28009858d7ro]

I received a 193 page PDF file that had obvious clues that it had been sanitized as 22 pages had been changed to full page sized rasterized images which are really ugly and hard to read. When I complained to the sender they denied that they had sanitized the file, insisting that the redaction process in Adobe Acrobat compresses PDF files. If that was true surely every page would have been affected, not just 22 pages in a 193 page PDF file.

From my own experiences I know that redaction can make a PDF file slightly smaller but I cannot believe that Acrobat would automatically compress the file during the redaction process.

[Abambo]

If you are redacting PDF files, that is for marking sensitive data in your file that you do not want to get published. It is, however, not a tool to compress a PDF file. The only compression that happens, is that the black squares will take eventually less space than the original data.

Also changing data to rasterized data does not happen with standard Acrobat operations on a PDF file. A normal text page will take in addition, less space than the same page as an image. If, however, in the original file, the pages were rasterized to begin with, it is possible that an intermediate compression operation did influence the quality of those pages, if you do not apply the correct parameters.

That's all I can say, without seeing the different PDF versions.

[Tom28009858d7ro]

"Also changing data to rasterized data does not happen with standard Acrobat operations on a PDF file ". Yes it does. This online PDF checking tool identifies the pages in the report that have become rasterized, "Page size 1190x1684 144DPI". I didn't sanitize this PDF file, when I received it, the sanitize had already been done. I am able to duplicate the issue easily enough by sanitizing a file that had been sent to me several years ago from the same source. Sorry but I can't share these files as they are part of a legal process now.