receiving goods - invoice vs. goods receipt document

Which document do I use for receiving goods - purchase invoice or goods receipt? Both seem to perform goods receiving...

Depending on your document flow. If you receive invoices / make payments to vendors only after goods are received then use Purchase Order -> Goods Receipt -> Purchase Invoice. Same if you want to separately track receiving goods and invoicing processes. On the purchase order you can see both invoiced and received quantities. If for you receive goods and receive a vendor invoice in the same transaction then you can just use vendor invoices.