how to create billing invoice and Barcode scan in products

Question

Hi

i am create billing system in c# windows application..

• Please tell me Billing System Procedure.
• how to add barcode with products 
•  how to scan barcode ?
• how to print in crystal report.
• how to export excel and pdf formate.
• how to convert .exe file with security.
• if any one theft my software please security and inform to my email or anything.

so, please tell me or any reference link. please .  please tell me as soon as possible.

 

 

thank you