Classic Winhelp

Winhelp is now obsolete and is not supported by default in Windows Vista. It was the original help format introduced with Windows 3.1 in the 1980s. It was improved slightly in the 32-bit version released with Windows 95 but not much has changed since then. Like HTML Help its primary purpose is to provide local help for applications installed on the user's computer.

Navigation in Winhelp is counter-intuitive (you cannot view a topic and the table of contents at the same time). Winhelp is RTF-based and formatting is not as flexible as HTML Help, and it is difficult to produce a Winhelp help file that matches the appearance of modern applications. Only use this format if you absolutely must for specific reasons.

Winhelp is not supported by default in Windows Vista:

Support for Winhelp is disabled by default in Microsoft Windows Vista. Even if your applications run under Vista, any calls to Winhelp help will simply produce an error message. Support for Winhelp can be added by downloading and installing the Vista version of the Winhelp viewer from Microsoft but developers are not permitted to distribute this update with their products. It is also possible that the operating system support for Winhelp may be removed in the future. We thus strongly recommend that you start transitioning to an alternative help format as soon as possible. See here for details

Features not supported by Winhelp:

Winhelp is a very old format and it has not been changed or upgraded for many years. It lacks support for a lot of modern formatting features. The following Help & Manual editor formatting features are not supported by Winhelp and should not be used if you plan to generate Winhelp output:

Chapters with text:	The Winhelp format does not support chapters with text. If your project contains chapters with text they will be exported twice: Once as a chapter without text and once as a sub-topic of the chapter without text, with the same name as the chapter. This "duplicate" topic will contain the content of your chapter with text. If you are outputting to both Winhelp and formats that support chapters with text you can use Help & Manual's conditional output features to create alternative topic and chapter versions for Winhelp and the other formats.
Complex tables:	Winhelp only includes extremely limited support for tables. You can only use very simple tables to arrange items in the topic page.
Table borders:	Table borders are not supported by Winhelp and will be invisible if you define them.
Nested tables:	Nested tables are not supported and will generate compiler errors when you publish to Winhelp.
Backgrounds and borders:	Winhelp has no support at all for background colors or borders. This applies to text, paragraphs and tables.
Superscript/subscript:	Winhelp does not support superscript, subscript or any other non-standard text decorations.

Features and pros and cons of classic Winhelp:

File extensions:	.hlp (help file) and .cnt (table of contents)
Format:	One HLP file for the help and a separate CNT file for the TOC
Platforms:	All Windows versions except Windows Vista (support in Vista must be installed manually by the user). The old 16-bit version of Winhelp is not supported because it is very buggy on all current Windows versions – it was only designed to run on Windows 3.0.
Typical use:	Local online help for applications installed on the user's local computer
Table of contents:	Yes, in a separate CNT file
Keyword index:	Yes
Full text search:	Yes
Context-sensitive help:	Yes, full support, including field-level popups
Popups:	Yes, fully-formatted popups with graphics, both in the help viewer and for context-sensitive help. In Winhelp popups can also contain hyperlinks.
Multimedia:	Multimedia support in Winhelp is very limited. Only standard Windows AVI videos are supported. Flash video and other video formats are not supported.
Printable by user:	Not really. The Winhelp viewer will only print single topics. Poor graphics print quality.
Pros:	Compact file format with strong compression, all graphics are packed in the HLP file, just as in HTML Help. Supported by virtually all Windows application development tools, easy to integrate with applications.
Cons:	Very unintuitive navigation. The navigation controls (Table of Contents, keywords and full text search) are in a separate window that cannot be displayed at the same time as the topic viewer. Less flexible formatting than HTML Help. Only supports BMP graphics (these are compressed, however). More difficult to produce help matching modern applications in appearance. Users are now generally more familiar with HTML Help. Only use Winhelp if you absolutely must.