Unless you have your own custom fields for First and Last Name, you would normally use Display Name which would automatically be set to:

• the Company Name
• the Individuals Name
• the Company Name followed by the Individuals Name

Examples:

• ACME, James Smith
• ACME
• James Smith

To get something like this:

Try this:

(object.state in ('draft', 'sent')  and 
 'Quotation - %s - %s' % (object.name, object.partner_id.display_name)
)
 or
'Order - %s - %s' % (object.name, object.partner_id.display_name)

Note: If the comma in the filename causes problems (it may with older software not written by our awesome Odoo developers), you can switch to the name field instead to just show the Company or Individual Name instead of the combination.​