Passwords in Adobe Acrobat
Standard PDF
security
Protected PDF document has
two passwords: an owner password and a user password. The document also specifies operations
that should be restricted even when the document is decrypted: printing;
copying text and graphics out of the document; modifying the document; and adding or modifying
text notes and AcroForm fields.
Applications for password recovery:
Password types
When the correct user
password is supplied, the document is opened and decrypted but these operations are
restricted; when the owner password is supplied, all operations are allowed. The owner password
is required to change these passwords and restrictions.
Encryption key
Protected PDF document is
encrypted with the RC4 algorithm. Encryption key length is 40 bits. Key is calculated
from the user password. Knowing of the owner password allows calculation of the user
password and therefore encryption key. All restrictions are enforced by software, not by PDF format itself.