And while some pros may scream and yell, I highly recommend writing your posts in a text editor with spell check and other features, so you can save it as you work along the way. When it is ready, then you can copy and paste it into your Write Post Screen.
I work in WordPerfect, but then I've totally changed all the quick corrects and auto correct features that turn every quote into curly cute things and such, which if kept in the file you post in your WordPress site, will turn into strange characters on the screen or, worse yet, bork your whole set up.
If you are a maven at WordPerfect and your word processing program and you understand what I'm talking about, then you can use it. If not:
DO NOT USE A WORD PROCESSING PROGRAM FOR WRITING POSTS
Just echoing the words of many of the other support mavens around here. They have to fix what gets screwed up when using word processors.
Otherwise, find a really good text editing program and try that.