Enterprise users can sync visits to Salesforce on a per-link basis: click on the Options button for any document link, and then click the Sync to Salesforce checkbox. We'll save the setting for future links so you won't have to select the option every time.
DocSend visits will sync with a Salesforce contact if the visitor's email address matches the contact's email address in Salesforce (recommended to "Require email to view" or use our Gmail/Outlook plugin). If the email does not match, but the DocSend and Salesforce account name matches, then DocSend will put the activity in that Salesforce account. If neither the email nor account matches, and the "Create new Leads for unmatching emails" is checked on, DocSend will create a new lead for you in Salesforce.
Note: Make sure your Salesforce account has the correct permissions for this to happen.