When requesting a Transaction PDF, use the requestJSON to pass the required transaction details, and the response will have responseJSON which stores the PDF response returned by NetSuite.
The requestJSON has the following parameters.
Pass the supported transaction type
Internal Id of the Transaction
Template Id of the PDF format stored in the NetSuite File Cabinet
External URL of the Script Deployed
Go through the following help article to generate the templateId and requestURL:
Supported Transactions Types:
Example to get the Invoice PDF (in a Blob content):