MS Word for Mac, insufficient memory

Forgive me if this has been touched on elsewhere - it's not popping up in my search.

I have an iMac, bought only a few months ago (if you need to know: 2.7GHz intel core, 8GB 1600MHz DDR3). The operating system is OX S version 10.9.4.

I run MS Word for Mac as part of MS Office. The version of MS Word is stated to be Word for Mac 2011 version 14.4.4.

I recently tried to save a version of a large file. I should point out that I'm a literary agent, and I often have to edit or re-format clients' manuscripts. The save operation failed, and I got a message on screen saying 'The save failed due to out of memory or disk space'. My immediate reaction was "Surely not!"

Is this some kind of fixable glitch, or do I really have an iMac with the memory space of a 1980 Atari?

Thanks in advance for any help.