Microsoft Word Doc to HTML converter
You can build a whole website using Microsoft Word, composing the pages then saving them as HTML files. This seems to be a simple solution but it's not the best practice to create web content. Word is a program originally meant to create print document sheets and not to compose websites. If you save a random .doc file, as .html extension, then open it with a plain text editor you will see a huge amount of ugly and unnecessary code at the beginning of the document and lots of inline styles which would overwrite the default styles of your website. See below the example source code from a Word document saved as .html file.
HTML Cleaner can convert Word docs to clean HTML for you with just a few simple clicks. Paste your document in the first input field, see the initial dirty code on the second editor, then click the Clean HTML button to execute the active cleaning operations. This way you'll get a much cleaner source than Word originally produces. You can also convert content with the same procedure from Excel, PowerPoint, .pdf, and even from other websites.
The best thing about this free online tool is that you don't have to browse your computer and upload any document to the server, just copy-paste everything. The conversion is processed on client side so your confidential code is never uploaded to the server and it can't be viewed by anyone else.
After you have finished cleaning the document you can preview the updated HTML code in the WYSIWYG editor. If you find any other modifications needed, just set up the cleaning preferences or use the find and replace tool to clean the code again until you reach the desired source.
WordHTML online converter
There's a dedicated website tailored for this type of document conversion which provides a very clean interface focusing on Word to HTML conversion: WordHTML.com. However it has HTML cleaning options, these are just secondary in this case. The website is also trying to raise awareness to the importance of the correct and clean article publishing.
An example from the source of an .htm file composed with Microsoft Word 2014: