@Ferdy 

After Purging an Envelope:

Once an envelope is purged, all associated documents.  The Certificate of Completion (COC) will be available if the purge does not include data redaction.  If it does it will be available, but all PII will be removed (redacted). 

After Closing an Account:

(I think you mean a user account) After an account is closed, access to all envelopes, including their Certificates of Completion, is terminated. An Admin on the account will have access to the COC and documents if they have shared access to the closed user.

By a Signer with No DocuSign Account:

A signer who does not have a DocuSign account can access the Certificate of Completion via the email they received when they completed signing the document. This link will typically remain available for a limited time, usually determined by the envelope's retention policy. The signer should download and save the COC for future reference​.

@JohnSantos 

Thanks for the clear answer.

Only one extra: with closing the account, I mean when a company decides to stop using DocuSign.

Are the COC of signed documents then still available somewhere to validate that the certificate in a signed PDF is a valid one?

Thanks.

@Ferdy 

When a company decided to stop using Docusign, the account will be closed 90 days after contract end.

All documents and CoCs have an embedded digital certificate to proof authenticity. You can validate it with any PDF software that has these capabilities, e.g. Adobe Acrobat Reader. It is long-term validated, so it can be validated regardless of it being present on the Docusign platform or not.

@JohnSantos 

Thanks for this clear answer.

Ferdy