Would it be possible to have the legal name of a contact pull through as the name listed on all documents generated - ie account sale reports, instead of just the general letters.

Otherwise just the client 'name' appears which may not be sufficient for accounting / legal purposes on all documents.

You do not always need to input a legal name, however when you do it is often because it is required. And you would want this legal name to pull through to all documents relating to this client/sale.
ie; If a Legal Name is available, use the Legal Name. If no Legal Name is available, use the Full Name

For the purpose of merging Library letters, this can be problematic as the merge fields need to be set within the template and if the Legal Name is set on the template it will not always merge data (unless the user is consistently entering in the Legal Name field on every contact). If the Full Name could be automatically copied into the Legal Name field on a contact, it would resolve this issue (and the user could update the Legal Name field as needed).