data entry simple - simple management way

we need a simple way to take care of our stocks and our article present in our workshop. this file have to be automated in scale stocks and automatically create a warning our of stock. the file need to give the user the capabilities to contain all clients,all invoices,all article, and finally have to be able to create an invoice and save them to the clients. the invoice need to be printable and downloadable in pdf the management is for a mechanic. other ask me tnks