For example, if you are not collecting Website field data on your forms, and your client fills in email@example.com, the link would point to www.salesforce.com.
If you asked for Website address on your form and the prospect's email were firstname.lastname@example.org but he listed his website as www.pardot.com, the company link would point to www.pardot.com.
Additionally, if a prospect does not have a value for the Company field, Pardot will display a Company URL in this field instead (this will not be synced to the CRM though). If there is a value for Website but not Company, Pardot will use the Website URL in the Company field. If there is neither a value for Website nor Company, Pardot will use the email address domain to determine the Company URL that will display in this field.
Note: When Pardot displays a URL in the Company field for a prospect, the URL is for display only. Unless the Company field is populated by either a) prospect's form completion, b) sync with CRM data, or c) manually by a Pardot user, automation rules or dynamic list criteria based on Company will interpret the Company field as Prospect Default Field / is empty.