picoCTF 2014: Redacted (Forensics) Write-up

Solve:

You found a letter that may shed light on recent events.

Redacted.pdf:

Hint:

That "super secret access code" looks interesting. I wonder if the info behind the black boxes is really gone for good?

Solution:
          In a letter, I have pdf file and in this file have black boxes to hidden text, It is a flag. when I read a hint, I find some tool to remove black boxes and I found Nitro PDF Professional 9 trial. It work.!!

1. Open PDF File.
2. Edit > Edit

3. Click and drag to remove black boxes, It will show the flag.

Flag: one_two_three_four