The document was too big to download,so it will need cropping, any ideas before I do this.?.
How will you crop it if you can't open it? An intact file is better if we are to verify what (if anything) is wrong with the file.
How are you opening the document--from the desktop, or from File > Open?
Did you try a fresh settings profile?
You can upload a large file to any of the free file-sharing sites and then paste a link to it here.