Can somebody help with this file? What is wrong with it?

I am very sorry to have to do this to you, but I can't find a better solution.

The attached file was typeset (transcribed) over a few sessions (OS X Yosemite, MS 2.0.3.), then I started proof reading when I noticed that MS was working very slowly (I mean very, several seconds for a command to be executed) and eventually once blocked my computer so I had to restart by turning off the power.
The file is quite large and it was a tad slow at the end of the transcription, but I am used to that. This is different. Can somebody take a look at the file and see if there is a problem?

Ir this is too much work let me know and I'll haveto delete it and start over.

I tried to find out how to open the backup file, but could not find it in the Apple documentation. Does anybody know how to do this on a Mac? (Apple's documentation isn't nearly as clear as the one for Musescore; apparently they think it is intuitive, hence no instructions needed...).