"The contractor to submit updated shop drawings for consultant review and approval"
My manager used to write such kinds of sentences with imperative sense in his mind. But, as far as I'm concern, this sentence doesn't have a main verb. An infinitive cannot function as a main verb in a sentence. So, the infinitive -to submit- cannot be the main verb in the above sentence. As a result, lacking a finite verb, how could we take above one as even a complete sentence whether imperative or not?
Moreover, such kinds of constructions are so familiar and widely used in senses other than imperative too. It's really confusing me.
Sentences are often 'reduced' in workplace documentation. Your example has the verb "is" omitted (The contractor is to submit ..."). It's stating a requirement, but it's not an actual imperative of course, more of a statement really saying what is expected of the contractor.