I have 3 annotating apps - iAnnotate, DocumentsToGo and Goodreader. After trying, I can say that none of them let me "scribble" on a Word (.doc/.docx) file. You can edit the file with the keyboard in all but Goodreader - but not write on it...
Have you considered using your computer to save the Word file as a PDF? Then you can use iAnnotate or Goodreader to write on the document.
Long story short: No, I don't know of an app that'll let you scribble on Word documents. Sorry.
Marilyn