Can I build a form that asks for a client id?

We send letters to our clients. Can I build a form that asks for a client id, then fills out the client data (name, address etc.) from a DB or .csv file?

We have a Spreadsheet to Form widget, it can populate form fields from attached excel file. Please check if this will work for you: How-to-Use-the-Spreadsheet-to-Form-Widget

Hope this helps! But, please get back to us if you need further assistance.