Due to the different technologies used in Microsoft Word and HTML used for help files, there are some rules to keep in mind when writing a help document. HTML does not support all features found in Microsoft Word, which may result in different formatting when the Word document is converted to HTML.
In the following you will find a summary of the major differences between Microsoft Word and HTML, and suggestions that help you formatting the document.
HTML has no concept of page sizes
On of the fundamental dissimilarities between Microsoft Word and HTML is that the page size in HTML can vary. When a HTML page is viewed in a browser or help viewer, a user may resize the HTML window.
Therefore, you cannot rely on the fact that a page has a certain boundary, which causes a paragraph to wrap at a certain word, etc. You need to ensure that the text in your document will flow properly regardless of the page size. This is especially important when working with floating images and other objects that do not flow inline with the text.
HTML is not desktop publishing
In Microsoft Word you have fined grained control over various aspects of the text layout, such as font size, line spacing, kerning, etc. By definition, HTML was not designed to allow such control. For instance, even though you specify a font size to be exactly 10 points, a vision impaired user may configure the HTML browser in a way that the font size is displayed with a much larger font size.
Therefore, you cannot expect the layout in HTML to be identical to the one displayed in Microsoft Word. You need to design your Word document in a way so that it is independent of the layout properties, such as font sizes, text wrapping, and picture sizes.
Tips and Tricks
Enabling Web Layout View
When editing your document, you can use the Web Layout view to display the document in a way it would be displayed in the HTML Help viewer.
To switch to the Web Layout view, click Web Layout 
on the View menu.
Showing Formatting Marks
The first step to quality formatting is to get an idea of what’s going on behind the scenes. Microsoft Word has a number of hidden formatting marks that indicate the position and kind of spaces, paragraph breaks, page breaks, and so forth. Showing this hidden information is often a great help, when it comes to discover problems with document formatting.
To show hidden formatting marks, click Show/Hide 
on the Standard toolbar.