Q.What is a 'Collateral Voucher'? How does it differ from a 'Primary Voucher'?

A collateral voucher is a stand-in for the missing original, and carries correspondingly weaker evidential value.

Contrast it directly with a primary voucher's status as the original evidence.

A Primary (original) Voucher is the documentary evidence in its first, original form — e.g. the actual invoice a supplier issued, or the actual receipt a customer was given.

A Collateral (secondary) Voucher is produced when the primary voucher cannot be obtained — for instance, a duplicate copy of an invoice, a certified extract, or a photocopy. Because it is not the original document, it is inherently less reliable evidence (it could, for example, be a duplicate created specifically to support a fictitious or altered entry), so the auditor must examine a collateral voucher with greater scrutiny and, where practicable, seek independent corroboration before relying on it.

Students sometimes treat a collateral voucher as equally reliable as a primary one simply because it 'shows the same information' — the point of the distinction is precisely that a COPY can be manipulated more easily than an original, so the auditor's level of scrutiny must differ.