Whether it be audio, video, published documents, etc. I'm always having trouble finding a program that will just do it all AND work every time. I stumbled upon CloudConvert, and I've used it with great success on dozens of different projects for myself and my students.
CloudConvert is free, it supports a multitude of different file types (148 to be exact), and it will send the documents to you in different ways, such as automatically emailing you the file when it's done converting. Everything is converted in the cloud, so it will not slow down your system while it is converting your files and documents.
It will also work with mobile, so if you have classroom tablets or mobile devices instead of computers, it will still work! The site is still listed as being in Beta, but as I've said, it's been awesome so far in my experience. Let me know in the comments if this is a useful site for you!
- CloudConvert: https://cloudconvert.org/