This page has been created for the purpose of helping users of CHM files figure out how to open those files under all combinations of Windows operating systems (Win 98 through Vista) and Internet Explorer browser versions. Unfortunately, this is a large task. If you don't find what you need on this page, see the note at the bottom.

Vista and Firefox: This writer reports no problems opening CHM files under Vista when those CHM files have been downloaded using Firefox instead of IE. This same writer has been happily using Firefox for quite some time, and would recommend it strongly--if only because of the CHM problems it circumvents. To repeat and clarify: CHM files downloaded using Firefox instead of IE appear to open and function perfectly fine under Vista. (This, of course, is in contrast to the same exact files that will not work if downloaded by IE7.)

Blocked: If the CHM files opens but displays a "content blocked" message on every page, it is—we think—because the file was tagged as "blocked" when it was downloaded to your PC. This is usually the easiest problem to find and to fix. Right-click on the CHM file, go to "Properties," and see if indicates that the file is blocked. There may be a message saying "This file came from another computer and might be blocked to help protect this computer." If so, just click on the "Unblock" box, and you should be in business.

Server Files: Content from CHM files that reside on network servers will frequently be blocked by Windows security features. Although there is a work-around for this, it is complicated and involves changing entries in the Windows registry. The much easier solution is to put a copy of the CHM file(s) on your PC.

Bad Path Name: CHM files will not work if their path or filename includes the pound (aka hash) character '#'. The hash character signifies an anchor in HTML so the CHM viewer fails to resolve the path properly and to retrieve the content. If this is your situation, move the file to a path that does not have a hash character in its name. In general, avoid using '#', '?', '&', '+', and other special characters in directory names.

Browser Issues: When you click on an external link inside a CHM file, the web page is opened with Internet Explorer and not with your computer's default browser. Why? Since the CHM viewer itself is a component of IE, or *is* IE operating in some special mode, the program does not issue a conventional call to the PC to use the default browser. Instead, since IE is already running and available, IE simply "tells itself" (?!!) to open the external page. There is no work-around to this "problem."

If the ideas and suggestions mentioned above do not resolve your problems opening CHM files, you might want to do a web search for "MJ's Help Diagnostics." This is a program that checks to see if the Windows programs and components needed to display CHMs are properly and completely installed on your (Windows) computer.