Dear teachers,

Would you please tell me what type of verb phrase is "are to be found" in the following sentence? (transitive or copular?)
I know that only transitive verbs can be used in the passive form, and yet I can't figure out what kind of sentence pattern is the following.

Many elements of the response are to be found in those documents.
Would you say that the obligatory prepositonal phrase "in those documents" is related to the subject or object "many elements"?

Thank you in advance.
'Be to' is called an idiom of futurity in Quirk. 'To be found' would be a passive infinitive.

We are to meet them at 8:00.
etc.
Hello, Mr Micawber

I understand that, but what would be the pattern of the sentence in that case?
a Direct Object (Many elements of the response) + a complex-transitive verb (are to be found) + an obligatory adverbial related to the DO (in those documents) an an implied subject ?

But if the subject of the sentence is "Many elements of the response", how can the verb be considered transitive? Does it become intransitive or copular?