Hi @RamaniBa ,
You might need to use a PDF library (e.g., Apache PDFBox) to sign the PDF using the key fetched from AWS KMS and a logic to verify the signature in AEM.
Apache PDFBox | A Java PDF Library
Also make sure proper IAM policies are set on AWS and a service user with necessary permission is created on AEM to achieve the requirement.
Hope this helps.
Regards,
Hemalatha C