Many people who come to the library need information in a different format then traditionally available for it to be accessible for them. Some online services do exist that can do this task however they are usually paid or have a limit to the number or size of documents that can be converted.
An example of an existing service is Sensus Access.

Your task is to make a file conversion tool that can convert a PDF to an MP3 file at the minimum as well as other file types where possible. The tool could be a mobile or web app. The tool itself must be accessible and be standalone without any limits.