We would like to an app that has two functions: 

1) Automatically copies Quotes.filename to Quotes.subject whenever Quotes.filename is updated. (we've renamed Quotes to offers in our CRM). 

2) Automatically copies 'Invoices.AH Invoice No' to 'Invoices.Subject' when a Quote is converted to Invoice (effectively when an Invoice is created I believe). 

 We don't know if this can be done via a Webapp or ZohoCreator - your recommendation is welcome.