On the Document page, you cannot delete a document if it is used on a message or if it has records and fields. However, if such a document is no longer desired, to clean up your environment, you can still delete it. On delete, only the document is deleted.
Usually, you do not clean up your documents frequently.
Beware
Cleaning up your documents permanently deletes them. Note that the messages in which the document is used cannot run until another document is linked to the message. So, use the clean-up functionality with caution.
Steps
Go to Connectivity studio > Periodic > Cleanup > Delete document.
In the list, find and select the desired document.
Click Delete.
Click Yes.
Close the page.