Changes in the versions:

2.21
  - Serious AES decryption bug fixed

2.2
  - Acrobat 7.0 (PDF 1.6) support including AES encryption and
unencrypted metadata feature (restrictions removal only)
  - 10-25% speed-up on Pentium 4 and AMD. Kernel crypto function
for any processor now can be easily added and the best rate
functions are chosen automatically. New /pXYZ option.
(n-clients version only).
  - 2-clients version instead of 1-client (for the same price) to use
the power of dual/dual-core processors. 
  - DEMO limitation changed, now FREE version doesn't stop but
produces the file with few readable pages. 

2.1a
  - Interruption by Ctrl+C bug on multiprocessor and P4 HyperThreading
    computers fixed (command-line versions only)

2.1
  - Few decryption bugs fixed

2.0
  - GUI version available, command-line is now full Win32 application
  - Engine fully rewritten, Acrobat 6.0 (PDF 1.5) support, no more
"String truncated" warnings (at least, up to PDF 1.4)
  - Pentium 4 optimization
  - More accurate estimated time calculation

1.2:
   - Acrobat 5.x (PDF 1.4) 128-bit encryption support - restrictions
removal only, files encrypted with user password can't be
guaranteed decrypted.
   - Few parsing bugs have been fixed.
   - First client now can be considered as "server". The decryption
is performed on this client only. New /1 option. (n-clients versions
only).
   - Demo limitations has been changed slightly, now it can decrypt
larger files.
   - Linux version available.

1.1:
   - /p option has been extended, now you can decrypt files with
known  onwer password instantly.  Restrictions  remover  version
hasn't been changed.

1.0:
   - key testing is 5% faster
   - new options /p, /y
   - fixed minor bugs in parsing and decrypting
   - some interface improvement

0.9:
   - First  (BETA) version  released.
