How to add pkcs1 signature to pdf by acrobat pro 7?

The default signature format is PKCS7 on Acrobat 7.
Through acrobat security admin guide for Acrobat 9 i can change the default signature format to pkcs1 on acrobat 9.
But i can not find the security admin guide for Acrobat 7,i tried the same method on Acrobat 7,but not success.
How can i change the default signature format on Acrobat 7.

Thanks.