A purchase quote can be used as a preliminary draft for a purchase order, which can then be converted to a purchase invoice.
When you have accepted the vendor's quote, you can convert it to a purchase order to process the purchase.
The purchase quote is removed from the database. A purchase order is created based on the information in the purchase quote, which you can use to process the purchase, and then post a purchase invoice. In the Quote No. field on both the purchase order and purchase invoice you can see the number of the purchase quote they were made from.
Note
It is not possible to convert a purchase quote to a purchase invoice directly, like it is possible with sales quotes. For details on how to create a purchase invoice, read Record Purchases with Purchase Invoices.