pdf link command button if then

[wrmedia]

created a command button that opens a pdf (c:\pdfs) with the same name as corder#

need to add code that will make the command button look in a different directory (c:\pdfs\lsi) if the vendor = LSI and open a pdf with the same name as vorder#

form has 3 fields

corder#
vendor
vorder#

and the command button

thanks