evince can't view pdf file 'test.pdf' as 'test'

["Yuandan Zhang" <yuandan.zhang@xxxxxxxxx>]

Hi,
when view a pdf file, for example, test pdf, 
evince test.pdf OK
xpdf test.pdf OK

when file name changed to 'test'
xpdf test OK (loaded as the pdf file), 
evince test => ERROR to load

evince seems can't see it as pdf file, but issues an error 
Unhandled MIME type: 'application/octet-stream'. 

How to configure it and make evince detect the pdf file, not only rely on the file name extension?

Yuandan