You can use tags in the PDF templates, emails, and in the notes and section notes of a quote, job, invoice, etc..
Standard Fields
Check the PDF template help for each module to see all the CRM tags - however, they are usually:
{InvoiceName} or {DeliveryName} or {ClientName}
{InvoiceAddress1}, {InvoiceAddress2}, etc.
Logo
{ClientLogo}
Custom Fields
Client custom fields should be prefixed with 'Client':
{ClientMyField}
Contact custom fields should be prefixed with 'ClientContact':
{ClientContactMyField}
Supplier custom fields should be prefixed with 'Supplier':
{SupplierMyField}