Windows Software Help Files Formats

• HTML (Online manual): Hypertext Markup Language
• CHM (HTML Help): Microsoft Compressed HTML Help
• HLP: Microsoft WinHelp
• PDF: Portable Document Format
• RTF: Rich Text Format & DOC: Microsoft Word
• TXT: Plain Text File
• Conclusion

Are you still wondering which help file format to use for your Windows software? The selection depends on your software and on the information that is in your help files. Each help file format has its own unique features that may be useful in certain situations. Generally, I would recommend that you use different help files for different situations.

To help you compare the formats at a glance, here is a summary table of their key characteristics:

This help file formats comparison shows that choosing the right help file format depends on your priorities — whether you need context‑sensitive help, offline access, or frequent updates.

How to choose the right format: a step‑by‑step decision algorithm

Here is a simple decision algorithm to help you select the right format:

1. Do you need context‑sensitive help (F1 or button‑based help inside your application)?
   • Yes → Choose CHM (native Windows support) or HLP (obsolete, avoid for new projects).
   • No → Continue to step 2.
2. Do users need to access the help offline without an internet connection?
   • Yes → Choose CHM, PDF, or RTF/DOC.
   • No → HTML online is the most flexible option.
3. Is printing the manual important?
   • Yes → Choose PDF (best print quality) or RTF/DOC.
   • No → HTML or CHM are better for on‑screen reading.
4. How often do you update your documentation?
   • Frequently (multiple times a year) → Choose HTML (instant updates) or TXT (simple edits).
   • Rarely (once a year or less) → CHM or PDF are acceptable.
5. Do your users work on multiple platforms (Windows, macOS, Linux)?
   • Yes → Choose HTML or PDF.
   • No → CHM is fine for Windows‑only users.

This help file format selection guide helps you choose help file format based on your specific requirements, not just general preferences.

HTML (Online manual): Hypertext Markup Language

The help system may consist of number of HTML pages. Each page is usually devoted to a specific topic and includes cross-links to other HTML pages. Often, there is a table of contents that allows fast navigation across the topic areas. Additionally, pages may contain special navigation links: next page, previous page, indexes, etc.

Usually the HTML help pages are uploaded on the product's Website. Creating online help is preferable if your software is platform independent and users can also read the help file in their Web browsers on any operating system. Storing help files as HTML pages on your web site is also useful if you frequently upd ate your documentation by adding new topics and pages. In this case, users do not have to download the entire help file after each upd ate to their computer.

Moreover, the online help manual which is a part of your website generates a targeted traffic. People can easily find your product because the online help allows your website to be more visible in relevant search results on search engines. The new visitors will consider your products seriously when they see a well made help system. Also, if a first time users experience difficulties with your software and needs technical support, you may easily resolve the issue by referring them to a particular page of your online help. With just one click, the users will see screenshots and explanations which will help them to solve the problem.

CHM (HTML Help): Microsoft Compressed HTML Help

CHM is a help format introduced by Microsoft in 1997. The CHM help file is a se t of web pages written in a subset of HTML and compressed together with LZX compression. The CHM file has a hyperlinked table of contents. It may also contain word indexes, and therefore, the CHM format is optimized for reading and searching.

The CHM file seems to be the most convenient way to deliver your software help in a single indexed file together with your program. Through the functions provided by hhctrl.ocx library, you may invoke HTML Help functions from any programming language. This HTMLhelp API allows opening a specific topic within the CHM file. Thus, with the CHM file you can easily implement a context sensitive help functionality in your software application.

Implementing context‑sensitive help

Context‑sensitive help allows your application to open a specific help topic when the user presses F1 or clicks a help button. Here is how to implement it with different formats:

• CHM: Use the HTML Help API (HtmlHelp() function) to open a specific topic by its identifier or URL. This is the most straightforward and well‑documented approach for Windows applications.
• HTML: You can implement context‑sensitive help by opening a specific URL in the user's browser (e.g., https://yourdomain.com/help/topic.html). However, this requires an internet connection and a web server.
• PDF and RTF/DOC: These formats do not support context‑sensitive help natively. You would need to build a custom mapping system that opens the document at a specific page — which is complex and rarely used.

For Windows applications, CHM remains the gold standard for context‑sensitive help because it is lightweight, fast, and works offline.

Context‑sensitive help implementation is a critical factor when choosing a help file format for Windows — and CHM is the only format that offers it out‑of‑the‑box with full API support.

For Windows users, this help file can be compiled with the HTML Help Workshop, which is distributed by Microsoft at no charge. Besides the HTML Help Workshop, there are commercial tools for creating CHM files faster and easier.

Although the CHM format was originally invented for the Windows platform, there are some tools which can read and navigate these files (e.g. xCHM, KchmViewer, GnoCHM, Chmox for OS X, or Chamonix for OS X), but they lack the various features of the Microsoft Windows tools.

HLP: Microsoft WinHelp

HLP (Microsoft WinHelp) is a proprietary format for help files that can be displayed by the Microsoft Help browser (winhelp.exe or winhlp32.exe modules). WinHelp 1.0 was introduced by Microsoft in 1990.

The source files require that you compile a .hlp file consisting of one or more Rich Text Format (RTF) documents and a help project file with the extension .hpj, along with any image files (.bmp, .wmf, or .shg) that are used within the Help file. An optional table of contents file with the extension .cnt can also be created for use with the .hlp file. The final help file can be compiled using a WinHelp compiler, which is distributed by Microsoft at no charge or by using a commercial help authoring program.

Although less advanced than the later CHM (Microsoft Compressed HTML Help) format, HLP remains a popular Help platform from the Windows 3.0 platform through to Windows XP. Support of HLP files was removed in Windows Vista; therefore the HLP file format is considered obsolete.

PDF: Portable Document Format

PDF is a document file format created by Adobe Systems in 1993 and is now being prepared for submission as an ISO standard. Each PDF file encapsulates the text, fonts, images, and vector graphics that compose the document. While PDF can describe very simple one page documents, it may also be used for multiple pages, complex documents that use a variety of fonts, graphics, colors, and images.

The PDF help file is preferable for platform independent applications because it is used for representing two-dimensional documents in a device independent and resolution independent fixed-layout format. PDF supports forms, links, and bookmarks that allow easy navigation in the document. Because PDF represents documents as a sequential se t of pages, it is convenient for printing. PDF supports encryption and digital rights management restrictions.

You can distribute your PDF help file with your software as well as store it remotely on your website. Web search engines, like Google, may index the text content of the PDF file and it will appear in the relevant search engine results.

There are many programs for creating PDFs, including the PDF printing capability built in to Mac OS X, the multi-platform OpenOffice.org, Microsoft Office 2007 (a free download from Microsoft is required), PDF print drivers for Microsoft Windows, and Adobe Acrobat itself. There is also specialized software for editing PDF help files, e.g. Dr.Explain.

RTF: Rich Text Format & DOC: Microsoft Word

RTF is a proprietary document file format developed by DEC in 1987 for cross-platform document interchange. Then, RTF format was purchased by Microsoft around 1990, who extended the standard. Most text processors are able to read and write RTF documents.

DOC (an abbreviation of 'document') is a Microsoft Word file format. Proprietary DOC files often contain more text formatting information (as well as scripts and 'undo' information) than files using RTF and HTML, but are usually less compatible.

Like PDF, RTF & DOC are good for printing documentation, while they may look slightly different in various readers on different operating systems, specifically graphics and embedded objects. These formats may be less convenient for complex documents with multiple pages and objects because of the significant amount of computer memory consumed while being displayed.

These formats may be created with numerous text editing software programs as well as with specialized help authoring software that supports RTF\DOC output.

TXT: Plain Text File

TXT is a computer file which contains only ordinary textual characters with essentially no formatting. Text file is meant to be read as is. The main disadvantages of using TXT files for help are: no graphics, formatting, or navigation. As a result, TXT is only preferable for short documents like installation and release notes and legal documents. Usually TXT documentation is distributed with simple and relatively small applications, like PDA programs or games. You may create a TXT file in any text editor.

Real‑world scenarios: which format works best for your application

In practice, you rarely use a single format. Here are four common scenarios and the format combinations that work best:

Scenario 1: Windows‑only desktop application with complex functionality

Distribute a CHM file with the application for context‑sensitive help (F1). Publish an HTML online manual on your website for users who prefer browsing without installing the app. Offer a PDF version for users who want to print the manual. This combination gives you the best of all worlds: fast in‑app help, searchable online documentation, and a printable reference.

Scenario 2: Cross‑platform or web‑based application

Use HTML as your primary documentation format — it works on any device and any operating system. Add a PDF download for users who need offline access or printing. Since your users are not tied to Windows, CHM is not a good fit. HTML and PDF are platform‑agnostic and accessible everywhere.

Scenario 3: Simple utility or internal tool with minimal documentation

A TXT readme file for installation notes and a short HTML page with basic instructions are often sufficient. Avoid over‑engineering documentation for simple tools. For small applications, heavy documentation formats like CHM or PDF are overkill. Keep it light and easy to maintain.

Scenario 4: Legacy application that must support older Windows versions

If you still support Windows XP or earlier, HLP may be your only option — but consider migrating to CHM or HTML as soon as possible, since HLP is obsolete and unsupported on modern Windows. This scenario is increasingly rare, but it still exists in some enterprise environments.

These software documentation best practices show that creating user documentation for Windows often involves a hybrid documentation approach rather than a single format.

Frequently Asked Questions about Windows Help File Formats

Can I use HTML help offline?

Not by default. HTML help requires a web server or a local browser to view. However, you can bundle HTML pages with your application and open them locally in the user's default browser. For true offline help with search and indexing, CHM is a better choice.

Is CHM still supported in Windows 11?

Yes, CHM files are still supported in Windows 11. The HTML Help viewer (hh.exe) is included with the operating system and continues to work. However, Microsoft has not added significant new features to CHM since Windows 7.

Can I convert my existing WinHelp (HLP) files to CHM or HTML?

Yes, there are tools that can convert HLP projects to CHM or HTML. However, the conversion may not be perfect, and you may need to manually adjust formatting, links, and images. Dr.Explain, for example, supports importing and converting legacy help projects.

Which format is best for searchability?

CHM has the most powerful built‑in search with full‑text indexing and ranking. HTML online help can be searched if your website has a search engine, but the quality depends on the implementation. PDF has basic search but no relevance ranking.

Can I use one source to generate multiple help formats?

Yes, with a help authoring tool like Dr.Explain, you can maintain a single source and export to CHM, HTML, PDF, RTF, and DOC — saving time and ensuring consistency across all formats.

These help file format FAQ answers address common Windows help documentation questions and help you avoid common documentation mistakes.

Conclusion

Evaluate how your software can be distributed and how people will use it. Do they need a context help file in the application or will they print out the entire help file and keep the manual on their desk? How often will you update the help file? Is it relatively easy to distribute together with your program files or is it better to store it on the website? Answering these questions will help you decide which format is best.

Often the combination of approaches will work best. You may keep the HTML manual on your website for reference and it may attract people from search engines, distribute the CHM file with the application for context sensitive help, and upload the printable version of the help file in PDF or RTF\DOC format on the public website for those who may want to print out the entire document as a reference.

Dennis Crane, the author of Dr.Explain, specializes in help authoring software development. He is online at http://www.drexplain.com

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