Add the following URL parameters to the page link to pre-populate firstname, lastname, email and phone number fields in forms:
?first_name={{contact.first_name}}&last_name={{contact.last_name}}&email={{contact.email}}&phone={{contact.phone_raw}}
e.g. https://somewebsite.com/somepage?first_name={{contact.first_name}}&last_name={{contact.last_name}}&email={{contact.email}}&phone={{contact.phone_raw}}
Passing other field values: pre-populate using the form field query key, e.g. Lead Source:
ls=linkedin
?first_name={{contact.first_name}}&last_name={{contact.last_name}}&email={{contact.email}}&phone={{contact.phone_raw}}&ls=linkedin