First, i think this question might help some people since it's a common mistake i see some companies make.
In our company, we have a list of partners, that must remain confidential. However, in order for our final customers to have access to our services, they have to signed up through a form where they need to inform in which company they work at. So we can verify their eligibility to our services.
One way of doing that would be creating an autocomplete field that helps them finding their company among our partners, but then anyone could search for all of our partner names through it.
Is there a way to do this and not providing access to our entire partner list?
You could ask for the email they have from their working company and compare the email domain to your partner list. If you find they match, you can send them an email with their specific eligibility/process... this way you validate their email and the company they work for in one step.