Often, if you need to specify the agent for a passive construction, you're probably better off using the active voice. I would prefer "Can we solve this problem?" and "Have you shut the door?" to either passive. Use the passive (without an agent) where the emphasis is on the action, not the person(s) performing the action.
This construction is present perfect passive.
When you talk about 'subjects' and 'objects' you must be careful that you do not confuse syntactic roles, the functions word or phrases play in a particular sentence, with semantic roles, the functions words or phrases play with respect to the meanings of verbs.
The core syntactic roles are subject, verb, and object. Every full sentence has a subject and and a verb; there will only be an object if the meaning of the verb and the form of the sentence require it.
A transitive verb like take, for instance, typically involves two semantic roles:
- the Agent, the person who performs the act of taking, and
- the Patient, the entity which the Agent takes
In an active sentence, the Agent is cast in the syntactic role of subject, the verb is cast in an active construction, and the Patient is cast in the syntactic role of object:
subjectThe kidnappersAGENT activeverbtook objectthe little girlPATIENT
In a passive sentence, however, the Patient becomes the subject and the verb is recast in the passive construction. The Agent may be omitted; if present, it is cast in the form of a preposition phrase headed by by:
subjectThe little girlPATIENT passive verbwas taken preposition phraseby the kidnappersAGENT
In your sentence
The passive subject (the 'Patient' who undergoes the action) is she.
The finite verb is the perfect auxiliary HAVE; it is cast in the present-tense form has and requires its complement to be cast in the past-participle form:
She has past participle ...
The next verb is the passive auxiliary BE; it is cast in the past-participle form been as the complement of the perfect auxiliary and requires its complement to be cast in the past-participle form:
She has been past participle ...
The final verb is the lexical verb TAKE; it is cast in the past-participle form taken as the complement of the passive auxiliary:
She has been taken.
The 'Agent' who performs the action is not expressed in your sentence.
Best Answer
Compare with the present tense:
The second of these is incorrect grammar. A passive form would be "A contract was signed by him". But there is no reason to use passive here.
So only "I believe that our manager has just signed a contract" is correct.
It would also be possible to say "I believe a contract has just been signed by our manager" but there is no need for the passive in this context.