"When you save Web pages format with Microsoft Word, additional tags are added so that you can continue to use the full functionality of Word to edit your content.
To reduce the size of Web pages, you can save them in filtered HTML. Filtered format removes Microsoft Office-specific tags. If you save in filtered HTML and then reopen the file in Office programs, text and general appearance will be preserved, but some features may work differently.
If you reopen a Web page in Word that you saved in filtered HTML, your text and general appearance are preserved, but you may not be able to use certain Word features in the usual way to edit your files. For example, the appearance of bulleted or numbered lists is preserved; however, some of the Word functionality associated with lists will not be preserved.
If you will need to edit the file later, you can maintain two files: one in Word format and one in filtered HTML format. You can edit the content in the Word document, save it in Word format for future editing, and then save a copy in filtered HTML format."