This isn't supported right now when using extensions. You should turn off extensions. This is something we ought to be able to support, so feel free to open a JIRA for it.
If you must use extensions and have other pdfs, the workaround is to map them to the default servlet. For example:
<servlet-mapping> <servlet-name>default</servlet-name> <url-pattern>/test.pdf<url-pattern> </servlet-mapping>