Best way to use a command button to display a pdf file

I am looking for advice on the best way to use a command button on a form to display a pdf file related to a certain field on the form.

The form is bound to a table named tblInvoices and the field on the form is "txtInvoice#" which is "Invoice #" in the table.

So for example, if the user has the form open to invoice # 123456 then when they click the command button I want the file named 123456.pdf to open.

--Steve