你对此保密可以翻译成You must keep this as secret吗？

看什么语境吧，如果是工作上比较正式的，就是 Please keep it confidential.
如果是朋友间的承诺，可以是: this is a secret between us,或者是更简单的:please don't tell anyone.
最好不用must，显得很生硬没礼貌。如果用Could you keep it as a secret?的问句，更容易被人接受 :)

You keep this information confidential

Do you have confidential

可以