The default crypt method for Type 4 is V2, which uses RC4
algorithm. Crypt method settings are in effect only when Type is 4 or higher.
The StringMethod and StreamMethod parameters can take any of the
following values:
 0 [None] – (Not supported)
 1 [Identity] – No encryption
 2 [V2] – Uses the RC4 algorithm
 3 [AESV2] – Uses the AES algorithm with 128bit encryption
keys
 4 [AESV3] – Uses the AES algorithm with 256bit encryption
keys
Adobe Reader does not support using more than one crypt method
per document (i.e. stringMethodâ‰ streamMethod). However, Identity is
degenerate and can be used with other crypt methods.
