Microsoft has dropped support for legacy help files with .HLP file extension in support for newer .CHM files. As a result, you cannot open the .HLP files on Windows 7. If you double click on an .HLP file in Windows 7, you would see an Open with… dialog instead of the actual help file. If you are using Windows 7 with the SP1 or a later service pack installed, then it shows you a message explaining why you cannot open those HLP files.
If you have an older software that uses legacy .HLP files, or you want to use any .HLP file, then you can add support for them by installing a downloadable patch from Microsoft. In the knowledge base article KB917607 Microsoft has detailed how the support for .HLP files has been dropped and how you can install a Windows 7 version of WinHlp32.exe.
The WinHlp32.exe program can be downloaded from Microsoft Download Center. The download requires a genuine Windows validation, or users can download using the following direct download links shown below :
Update (October 2020): Windows has stopped all support for Windows 7 and the above links from Microsoft website no longer work. We have replaced the links with third-party site links.