@Karan are you looking to just generate the default PDF, or to use a different PDF template? If you want to open the default Cash Sale PDF in a new tab, you can do so very easily with a custom transaction body field, no script required. Just create a new transaction body field of type Hyperlink, store value unchecked, formula unchecked, and default value of:

<https://ACCTID.app.netsuite.com/app/accounting/print/hotprint.nl?regular=T&sethotprinter=T&trantype=cashsale&id=>{id}