वित्तीय लेन-देन को रिकॉर्ड करने के लिए निम्नलिखित में से कौन सा एक स्रोत दस्तावेज़ (Source Document) है?

Salal received a document from Cullen's Stationery Supplies billing them for eight reams of paper, which were delivered previously. How would Salal classify and record this document?

What is the primary purpose of a purchase invoice from a buyer's perspective? (i) To claim back the input sales tax/VAT (ii) To identify the specific goods or services bought (iii) To record the exact amount owed to the supplier (iv) To record how much is owed from the customer