这是一份机密文件，请妥善保管。

Zhè shì yī fèn jī mì wén jiàn, qǐng tuǒ shàn bǎo guǎn.

This is a classified document, please handle it with care.

这些资料属于公司机密，你不能随便带走。

Zhèxiē zīliào shǔyú gōngsī jīmì, nǐ bùnéng suíbiàn dàizǒu.

These materials are company secrets; you must not take them away casually.

会议内容非常机密，只有少数人知道细节。

Huìyì nèiróng fēicháng jīmì, zhǐyǒu shǎoshù rén zhīdào xìjié.

The content of the meeting is highly confidential, and only a few people know the details.