# Blank Paper

We're given what is supposed to be a PDF document, but can't be opened as it is missing its magic number, or signature, which denotes that it is indeed a PDF file. This is evident when we open up the file in a hex editor such as Bless.


The first four bytes are missing. PDF files have a signature of `25 50 44 46 2d`.

You can see a list of file signatures here: [Wikipedia](https://en.wikipedia.org/wiki/List_of_file_signatures)

To fix this, we can simply just add the signature.


Original writeup (https://github.com/shawnduong/ctf-writeups/blob/master/2019-ANGSTROM/Misc/blank-paper.md).