Considerations for help systems for web applications.

• User count If there aren’t many users, a simple text file should suffice. The next step up could be a word processing document or PDF. HTML is probably too cumbersome and costly for a small user base, unless it is expected to grow.
• System complexity Simple systems, or those with excellent user interfaces need less documentation. Complex systems require more. Use the appropriate references to assist the user not only in using the application but working well in the system. For example, if they will be classifying information, provide links to materials that will help them enter the right data, not just valid data. This data should be separate, so it can be maintained by the appropriate people.
• Target user type Internal users may be fine with a printed piece of paper. Other users may need a PDF, that they can search and print, and use familiar navigation. Potential clients should see the very finest help resources, because the content, navigation, presentation, and access to information may determine whether they purchase the product or not.
• Features Should people be able to navigate between pages? Should they be able to search? Is a table of contents or index necessary? Type size should be considered, as well as whether images are important.
• Images Screenshots should probably be avoided, since they may change and that requires documentation updates.
• Author/Editor/Producer/Maintainer The person that produces the document should have the requisite skills. If it is an HTML document, the editor must know how to write decent HTML, including any necessary features.
• Production The amount of effort and cost should be considered.

I think an excellent solution is a PDF, for the following reasons:

• It is a popular format and the reader is a trusted piece of software
• It has search and zoom
• You can have tables of contents and indexes that link into the document
• They print well
• You can protect them from copying
• You can link into them with anchors - into pages and sections
• They are cost-effective to maintain and simple to track