Convert an Indesign Template (serial letter) to a PDF, variables must be fillable via PHP/MySQL

We are an IT refurbishing company, and took on a new business field in the last year. We sell our products, refurbished laptops via already existing shops in a kind of commission sale. As this business field developed better than expected we are now changing processes and are developing a web-based system to handle everything. In the moment our partners get the receipt pre-printed with every laptop. This is done via a serial letter in Indesign, fed with data we exported from our merchandise management system. To avoid this detour in the future we want the newly built system to create PDF receipts matching our corporate design rules. So I would need a PHP/PDF professional, able to transform the Indesign template into a PDF template that can be filled on the fly with data from MySQL/PHP. This should be done via any free PDF library.