Security for signed PDF documents

Hello, We want to use Adobe sign on a platform called Salesforce. Fortunately, we are already linked and have downloaded the trial version from AppExchange and are in progress.

An important part of this is the security of the signature document.
The guide confirmed that you can edit the signature document only if you set the permission password in Acrobat DC and the user enters the password.
But I've confirmed that I can edit a copy of the signature document using a PDF editing tool called Wondershare PDFelement.
Is this case possible because I didn't set the authorization password?

In Salesforce, there was a password setting for viewing documents, but I didn't see the password setting for permission. Can I set it up in Salesforce?
What should I do to prevent recipients from editing a copy of the signature PDF?
And we are a Korean company. Do you have a case of applying Adobe sign in Korea?