Be + past tense of the verb

It's not always followed by a past tense:

Be happy.

Be aware that lions are in the park.

Be sure to leave the door open.

Yeah, thanks. Someone told me that "informed" is used here as an adjective.
The thing is I am trying to help someone who erroneously wrote "Please be inform..." rather than "Please be informed..."

Any explanations?

You should provide more context for the situation where the person wrote,

"Please be inform...".



First, it is never the "past tense form". It is the past participle form.

I want you to be informed.

*I want the best plan to be chose.*

[*....* denotes ungrammatical]

I want the best plan to be chosen.

The reason that you see the past participle [NOT THE PAST TENSE] used with 'be' is that the meaning is a passive one.

I want that to be done by Friday.

*I want that to be did by Friday.*

[*....* denotes ungrammatical]