c# - Determine if a byte[] is a pdf file

Question

Is there any way of checking if a byte[] is a pdf without opening?

I have some code to display a list of byte[] as pdf thumbnails. I previously knew all the byte[] were pdf's because we filtered the servlet to only return these. Now the requirement has changed and I need to bring all file types back. Is there any way of checking what the byte[] is, or more specifically determining if it isn't, a pdf?

Answer 1

Check the first 4 bytes of the array.

If those are 0x25 0x50 0x44 0x46 then it's most probably a PDF file.