Sorry for the late reply. We have investigated the issue in detail and it is still working for some platforms (e.g. check https://api.aspose.com/v1.1/words/Sample.docx?format=pdf&appSID=7781c7b2-170c-4ae1-a5fc-80fe35be6807&signature=y-s0PqX4df3zXZaoXM34I4OaAT8=) so that is not an issue with the service. It looks like Sign method is not working as expected for HTTPS after the last service update.
Can you please share which development language/platform are you using? We will try to resolve this issue for that platform as soon as possible. In the meantime, can you give another try to HTTPS and confirm if it is still not working for you?
The issue is resolved. Please try again and let us know it is fixed at your end as well.