It is possible to automatically pre-populate WFFM forms with Salesforce Contact (or Lead) data if the S4S Security provider has been implemented. In this scenario users log into the Sitecore website using credentials stored in the Salesforce Contact (or Lead) record. The Sitecore profile information is also stored in the contact record and can be rendered to the WFFM form using the standard Sitecore Rules settings as in the example below. A separate rule can be applied to each WFFM form field.
Using a Custom Save Action DLL (Pre-Sitecore 9)