Use Estimate when you only want to send a quote.
Use Challan when goods move now but final billing is not ready yet.
Use Invoice when billing is final and should affect final sales records.
Use Purchase Order when you are ordering goods from a supplier.
Use Purchase Invoice when the supplier bill arrives and the purchase is final.
Whenever possible, convert from one document to the next instead of typing the same data again.
Review any pending or confirmation banner before you finalize the next stage.

Tip: Explain this rule to every operator once: quote is Estimate, goods movement is Challan, final bill is Invoice.

Important: A wrong document choice can create wrong stock, wrong pending status, or wrong GST understanding.

Using the correct document type prevents wrong stock movement and reporting confusion.