Microsoft Word is a fine word processor for producing documents to be shared or printed, with a wealth of print-based options for indexing, and producing table of contents. As a web publishing tool it is a little less than ideal and produces very messy HTML. The same applies when using Google Docs, OpenOffice, or other word processors.
When text is pasted it initially looks fine:
But looking at the HTML code you can see that it is full of additional tagging information.
This could cause issues with the display of the post or page on your blog, and effect the general layout, as well. The same code above can be written a lot more cleanly using the WordPress visual editor:
Using Word Cleanly
If you decide that you still want to use Word then you should use the Word cleanup feature to remove all extraneous tags from your text. From the visual editor click on the show kitchen sink button:
Then click on the paste Word button:
A window will appear where you can insert your Word content.
When satisfied, you can then click insert and it will clean the content and insert it into your post. Note that all your formatting will be removed so any styles will need to be added in afterward.
Note that you will have to upload any images that were in the Word document to your blog before you can use them. See the Images page for more information about this.