tells you all about encoding. Apparently, this document is either encoded or corrupted.

If it's corrupted, the best thing to do is to go back to the last good backup. If it's encoded, either you did it yourself or somebody else did it. Anyway, if you don't know which of the possible codes it is, just try all. Or install the right fonts, as mentioned in the above article. Or go back to the last backup that isn't encoded.

Hope this helps.