expression, godan verb (-su)
affix one's seal; stamp one's seal
Used when physically pressing a personal seal (印鑑) onto a document or surface to authenticate or approve it.
契約書に印を押すのを忘れないでください。
Please don't forget to affix your seal on the contract.
Similar meaning, but 判を押す can also mean 'to stamp' in a more general sense, while 印を押す specifically refers to affixing one's personal seal.
Compound of 印 (seal) + を (object marker) + 押す (to press).