Think about who writes the purchase indent and who receives it. It is raised by a user department such as production or stores, and it is sent to the purchase department of the very same company, simply asking that department to buy certain materials. It never travels to an outside party the way a purchase order does, it creates no legal obligation the way a contract does, and it has nothing to do with property ownership. Because it stays entirely within the organisation, it is classified as an internal document.
We can also reach the answer by tracing the purchasing cycle step by step and locating exactly where the indent sits in that flow.
Tracing the cycle this way confirms the indent belongs to the very first, purely internal stage of procurement.
Therefore, the correct answer is Internal document.