Enclosing (e.g., with a letter) — to put additional documents or items together inside an envelope or package.
申込書を封筒に同封して郵送してください。
Please enclose the application form in an envelope and mail it.
履歴書を同封のうえ、ご応募ください。
Please apply with your resume enclosed.
請求書を同封しましたので、ご確認ください。
I have enclosed the invoice, so please check it.