Grammar note:
When modals are used to talk about past events, the modal is followed by the perfect infinitive, without 'to'.
The perfect infinitive is made with 'have' + the past participle of the main verb. Here are some examples of modal verbs followed by perfect infinitives:
must have left
might have stolen
may have taken
could have dropped
Remember, if you don't use a modal, then you are giving a fact, for example: I left it in the shop.
Be careful: Modal verbs often have other different meanings. For example, 'could' can be used to show ability as well as possibility. Use the context to help you understand which meaning is being used. 'Can' is NOT normally used to talk about the past: use 'could'.
Vocabulary:
the paperwork:
official documents, usually connected to a business transaction