How to correct sign a pdf (PADES) to have Multiple Signatures on same pdf file?

Would you have an example of what would be the correct procedure to sign the same file with two different certificates?

When i open in acrobat the file signed 2 times with 2 different certificates, adobe shows me that the first signature was deleted from the file, what would be the correct way to sign the file in order to get two valid signatures?

There is no code in the library to do that. I am afraid you have to write your own code.