Mail merge on a website

I have an Excel spreadsheet with around 60 fields and a Word mail merge doc which I have been using for many years. I used to generate individual files and send them to users. I now need to automate this and take it into my website. Eg: A user enters his Employee ID into a field on the website and if it's correct, his corresponding file (Excel row) has to be merged and given for download. I need to be able to change the merge document template if required to add or delete fields. That's it.