If you were writing it in plaintext you could use the 'wc' terminal command. 'wc -w' will tell you the number of words in a document (-l will give you the number of lines, -c the number of characters). However, if it has formatting, the results will not be accurate because the file with have other crap in it besides what you've written. One solution would be to copy and paste what you've written into a plain-text document and then use wc.