How to fetch data from 2 forms in HTML

How to fetch data from 2 forms in HTML

Question about fetching data...

I have 2 forms - called "Customer" and "Purchase"

Purchase form has a lookup field for my employees to enter in Customer name (if already in Customer form), or enter in a new customer.  When Purchase form is submitted, an HTML page is opened from which we can print out a sales receipt that the customer signs etc.  This HTML page has data fetched from the currentRecord (for Purchase), but I would also like to have it put the customer information (their name, address, etc) on it.  I know I can easily put the customer's name on it - because there is already a lookup field that populates their name, but I'm unsure of how to get more of their info on it.

Thanks for any ideas!