In each client, there is a Contacts tab where you can manage all the contacts (Project Managers or other) for this client.
You can easily add a new contact (using the 'Add a contact' button) or edit the existing ones (by clicking on the three dots at the end of each line).
You can add notes for each of these contacts, define if they should automatically receive the invoices and quotes you send to this client, and give a 'friendly name' to the contact (see this article: https://help.lsp.expert/en/articles/2258450-when-i-send-a-document-to-a-client-supplier-can-i-define-how-this-person-should-be-named-in-the-email).
Then, once you're in the document itself, you can easily send this document to the contacts concerned by clicking on Actions > Send email.
You'll arrive in the sending screen, where you see that the contacts concerned are ticked (depending on the type of document and on what you defined at the client level). You can of course untick them and add a new contact (with an automatic update at the client level).
