🚀 go-pugleaf

      first i use the sdk of version 7




That's OK. 7 supports everything from 40 - 128 bit RC4 and I believe 128-bit AES as well, but I'd have to verify that. RC4 for sure.

      so,at first i should find a way to solve the decrypt the pdf file,and
      then i can do some other work at that base




Acrobat's internal encryption does not expose raw methods for handling various encryption forms - it only has APIs for using it's own forms of encryption. You will need to choose an open-source encryption library that supports the algorithms you want to provide your users with, or write your own from scratch. Personally I recommend the crypto++ libraries - I have used it with much success in the past, but there are many other great options as well.

For the workflow you are describing, most of your development won't have anything to do with Acrobat. You'll need to do the file recognition and decryption entirely using non-SDK methods and libraries, and how you do this will depend entirely on which crypto library you decide on.