In the company that you want to apply a PACT against, go into the Contract/PACT Button > PACT tab. Enter the vendor's name and the PACT account number. When the best price files are picked up for the selected vendor, the PACT item list and prices will also import into this area.
If you would like the PACT prices to apply to several customers, you can click the share button at the top, and add as many customers to share this PACT as required.