Simplest solution. Create the text in the wordpress editor using upper case where needed to begin with, or create it in a plain text editor and paste it from that.
Second possibility: Add a class to your style sheet to transform the text to uppercase. Example:
Then wrap the text you want in upper case in a div with the class of "myclass".
Third possibility: Create your document in MSWord. Try pasting it in the editor using the "Paste as Plain Text" tool in the tool bar, and see if that makes any difference.