Can AI simply outline everything in a PDF rather than preserve text as text?

I’m on a 2013 MacBook Pro running Mavericks using CS4.  I am a composer of experimental music.

My workflow is as follows:  I create a music score in a program called Sibelius - I export the file as a PDF - I open this PDF in Illustrator and edit it further. 

This usually works great but occasionally I suddenly get the following error when I open a file: “to preserve appearance, some text has been outlined”. When I proceed to open the file the musical notes have been replaced with text letters and nothing as been outlined.  In Sibelius, musical notes are actually text from a special font called Opus.  I don’t care if AI treats the notes as text or simply as outlined objects as long as they look right and can be moved around. 

Is there a way to make AI look at a PDF and not try to preserve the text but simply outline everything as individual objects so that they look the same as in the orignal PDF?

Thanks