Ariadne is an Open Source system, which means you can change anything you like (or hire someone to do it for you). Since Ariadne is built in PHP, one of the most popular and easy to learn programming languages around, it is not too difficult to extend Ariadne for whatever you need it to do.
But extending Ariadne is usually not necessary, it supports many open standards and protocols out of the box. It supports in no particular order: HTTP, FTP, SOAP, WebDAV, XML, XML-RPC, RSS, CSV, PDF, etc. You can export content from Ariadne as WDDX, so even if you want to migrate to a different system Ariadne makes it as easy as possible.
Ariadne also understands Word, Excel and PDF documents. Ariadne's full text search will happily search through the contents of such uploaded documents.
If you have an ActiveDirectory or LDAP server in your organization, Ariadne can connect to it and let you log in with your existing username and password.
Finally Ariadne can connect to virtually any database system around, so you can easily mix existing information into your Ariadne website or application.