We have a customer who has lots of PDF documents all with AES-256 encryption set on them. However one product doesn't support 256 yet, so would your product work by batch amending all AES-256 to AES-128?
many thanks
Customer
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Yes, this is possible, you may use following steps to try,
1. You can use VeryPDF PDF Password Remover software to remove AES-256 encryption from your PDF files first,
https://www.verypdf.com/app/pdf-password-remover/index.html
2. You can use "VeryPDF PDF Security and Signature (Shell & COM & SDK)" to set AES-128 encryption to these PDF files again,
https://www.verypdf.com/app/pdf-security-and-signature/try-and-buy.html
for example,
pdfsecure.exe -newencrypt "--encrypt 123 456 128 --force-R5" D:\test.pdf D:\out.pdf
pdfsecure.exe -newencrypt "--encrypt 123 456 128 --print=full --modify=none" D:\test.pdf D:\out.pdf
pdfsecure.exe -newencrypt "--encrypt 123 456 128 --force-R5 --print=full --modify=none" D:\test.pdf D:\out.pdf
"-newencrypt" is an new encryption option, you may use it with following options,
Encryption Options for "-newencrypt" parameter.
To change the encryption parameters of a file, use the --encrypt flag. The syntax is
--encrypt user-password owner-password key-length [restrictions] --
Note that "--" terminates parsing of encryption flags and must be present even if no restrictions are present.
Either or both of the user password and the owner password may be empty strings.
The value for key-length may be 40, 128, or 256. The restriction flags are dependent upon key length. When no additional restrictions are given, the default is to be fully permissive.
You may also look at following web pages for more information,
VeryPDF