Show HN: PDFs that are readable by human eyes only
This is broken in multiple ways, some obvious, some not.<p>1. Obviously most people jumped directly to OCR, and that works of course. So counter to the OP, you can trivially render the first page to a high resolution PNG and then OCR that with what will probably be 100% accurate results. Sample image: <a href="https://i.imgur.com/hyJOSjY.jpg" rel="nofollow">https://i.imgur.com/hyJOSjY.jpg</a><p>2. This is just messing with glyphs in fonts, so one trivial way of undoing the changes <i>losslessly</i> (not even requiring OCR) is to create a mapping between each font glyph and the original character. For example, I was able to extract the font used for the text "CONTENTS" near the beginning of the sample document. It is named "SecureFont-1845559949-FranklinGothic-Demi", as extracted by mutool. In the PDF "CONTENTS" is made up of eight Unicode characters, which render as "CONTENTS" in that font.<p>3. Even if the first two methods somehow failed, the same character in a given font is repeatedly used to render the same character in English. That makes the approach similar to a substitution cipher [1] which is trivially broken with frequency analysis. You could literally just copy / paste the fake "text" out of the PDF and with an analysis tool derive the original text. This isn't really significant since the PDF can be read by sight anyway, but it's worth pointing out.<p>[1] <a href="https://en.wikipedia.org/wiki/Substitution_cipher" rel="nofollow">https://en.wikipedia.org/wiki/Substitution_cipher</a>