I'm looking at adding a feature to enable users of a web application to be able to view, download and upload documents that are attached to an item in the web site.

This is not a shopping cart site. :-)

The site/application is designed on Linux/Apache/MySQL/CouchDB/HTML5/CSS/JS/JSON/PHP.

I'd prefer an attachment/file management solution to work with the above technologies if possible.

The documents could be in any number of formats, such as PDF, DOCX, XLSX, PPT etc.

What do you more experienced (than me) people suggest?

Many thanks!