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Microsoft Compiled HTML Help
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<h2 id="history">History</h2> <p>CHM was introduced as the successor to <a href="/facts/Microsoft_WinHelp/qf1N6Sxu">Microsoft WinHelp</a> with the release of <a href="/facts/Windows_95/1E1L93qC">Windows 95 OSR 2.5</a>. Within the <a href="/facts/Windows_NT_family/EtccWvxQ">Windows NT family</a>, the CHM file support is introduced in <a href="/facts/Windows_NT_4.0/EcKYxrkx">Windows NT 4.0</a><a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a><a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> and is still supported in <a href="/facts/Windows_11/J2ywV8r4">Windows 11</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> <table><tbody><tr><th>Month</th><th>Year</th><th>Description</th></tr><tr><td>February</td><td>1996</td><td><a href="/facts/Microsoft/nGIDDXdx">Microsoft</a> announces plans to stop development of WinHelp and start development on HTML Help.</td></tr><tr><td>August</td><td>1997</td><td>HTML Help 1.0 (HH 1.0) is released with <a href="/facts/Internet_Explorer_4/ztoV77jR">Internet Explorer 4</a>.</td></tr><tr><td>February</td><td>1998</td><td>HTML Help 1.1a ships with <a href="/facts/Windows_98/6qtq4oJm">Windows 98</a>.</td></tr><tr><td>January</td><td rowspan="2">2000</td><td>HTML Help 1.3 ships with <a href="/facts/Windows_2000/amJIt9gz">Windows 2000</a>.</td></tr><tr><td>July</td><td>HTML Help 1.32 releases with <a href="/facts/Internet_Explorer_5/HaSYzQEg">Internet Explorer 5.5</a> and <a href="/facts/Windows_Me/fjENFRNa">Windows Me</a>.</td></tr><tr><td>October</td><td rowspan="2">2001</td><td>HTML Help 1.33 releases with <a href="/facts/Internet_Explorer_6/MGfbdL4h">Internet Explorer 6</a> and <a href="/facts/Windows_XP/IozrkAYS">Windows XP</a>.</td></tr><tr><td>March</td><td>At the WritersUA (formerly WinWriters) conference, Microsoft announces plans for a new help platform, Help 2, which is also HTML based.</td></tr><tr><td>January</td><td>2003</td><td>Microsoft decides not to release <a href="/facts/Microsoft_Help_2/65kqKm6n">Microsoft Help 2</a> as a general Help platform.</td></tr></tbody></table> <p>Microsoft has announced that they do not intend to add any new features to HTML Help.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="file-format">File format</h2> <p>Help is delivered as a binary file with the .chm extension. It contains a set of HTML files, a <a href="/facts/Hyperlink/LqNsa84e">hyperlinked</a> table of contents, and an index file. The file format has been reverse-engineered and documentation of it is freely available.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a><a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p><p>The file starts with bytes "ITSF" (in <a href="/facts/ASCII/vGUI33Qu">ASCII</a>), for "Info-Tech Storage Format", which is the internal name given by Microsoft to the generic storage file format used for CHM files.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>CHM files support the following features: </p> <ul><li>Data compression (using <a href="/facts/LZX/XpUz9NNB">LZX</a>)</li> <li>Built-in search engine</li> <li>Ability to merge multiple .chm help files</li> <li>Extended character support, although it does not fully support <a href="/facts/Unicode/DDu3MfPV">Unicode</a>.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li></ul> <p>The <a href="/facts/Microsoft_Reader/maho7MPd">Microsoft Reader</a>'s .lit file format is a modification of the HTML Help CHM format. CHM files are sometimes used for e-books.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h2 id="viewers">Viewers</h2> <p>In addition to Microsoft Windows, the following apps support CHM: </p> <table><tbody><tr><th>Name</th><th>Operating system</th><th>Website</th><th></th></tr><tr><td><a href="/facts/Okular/qSFEHo9M">Okular</a></td><td>Windows, Linux, Unix-like</td><td><a href="https://okular.kde.org/">okular.kde.org</a><p><a href="https://invent.kde.org/graphics/okular">invent.kde.org/graphics/okular</a></p></td><td>Uses hh.exe on Windows</td></tr><tr><td><a href="/facts/Calibre_(software)/HHFeh7Lf">Calibre</a></td><td>Windows, macOs, Linux,</td><td><a href="https://calibre-ebook.com/">calibre-ebook.com</a><p><a href="https://github.com/kovidgoyal">calibre</a> on <a href="/facts/GitHub/n1hNCsc3">GitHub</a></p></td><td></td></tr><tr><td><a href="/facts/Sumatra_PDF/UzLm20GT">Sumatra PDF</a></td><td>Windows</td><td><a href="https://www.sumatrapdfreader.org/">www.sumatrapdfreader.org</a><p><a href="https://github.com/sumatrapdfreader">sumatrapdf</a> on <a href="/facts/GitHub/n1hNCsc3">GitHub</a></p></td><td></td></tr><tr><td>GnoCHM</td><td>Linux, BSD</td><td><a href="https://sourceforge.net/projects/gnochm/">GnoCHM</a> on <a href="/facts/SourceForge/lxYAgUAX">SourceForge</a></td><td></td></tr><tr><td>CHM View</td><td>None/Uncompiled</td><td><a href="https://github.com/ojuba-org">chmviewkit</a> on <a href="/facts/GitHub/n1hNCsc3">GitHub</a></td><td></td></tr><tr><td>kchmviewer</td><td>Windows, Linux</td><td><a href="https://ulduzsoft.com/kchmviewer/">ulduzsoft.com/kchmviewer/</a></td><td></td></tr><tr><td>KCHM</td><td>Linux, BSD, Solaris</td><td><a href="https://sourceforge.net/projects/kchm/">KCHM</a> on <a href="/facts/SourceForge/lxYAgUAX">SourceForge</a></td><td></td></tr><tr><td>CHMPane</td><td>Windows, macOS, Linux</td><td><a href="https://sourceforge.net/projects/chmpane/">CHMPane</a> on <a href="/facts/SourceForge/lxYAgUAX">SourceForge</a></td><td></td></tr><tr><td>CHMate Neue</td><td>iOS, iPadOS, visionOS</td><td><a href="https://itunes.apple.com/app/chmate-neue-chm-reader-reloaded/id335157929">CHMate Neue</a> on <a href="/facts/ITunes/pdXPE33T">iTunes</a></td><td></td></tr><tr><td>iChm</td><td>iOS, macOS</td><td><a href="https://itunes.apple.com/app/ichm-chm-reader/id1243909868">iChm</a> on <a href="/facts/ITunes/pdXPE33T">iTunes</a></td><td>Discontinued</td></tr><tr><td>ChmPlus</td><td>iOS, iPadOS, macOS, visionOS</td><td><a href="https://itunes.apple.com/app/chmplus-pro-chm-reader/id441521818">ChmPlus</a> on <a href="/facts/ITunes/pdXPE33T">iTunes</a></td><td></td></tr><tr><td>Chmox</td><td>macOS</td><td><a href="http://chmox.sourceforge.net">chmox.sourceforge.net</a><p><a href="https://sourceforge.net/projects/chmox/">Chmox</a> on <a href="/facts/SourceForge/lxYAgUAX">SourceForge</a></p></td><td></td></tr><tr><td>Clearview</td><td>macOS</td><td><a href="https://itunes.apple.com/app/clearview/id557090104">Clearview</a> on <a href="/facts/ITunes/pdXPE33T">iTunes</a></td><td></td></tr><tr><td>DisplayCHM</td><td>Linux</td><td><a href="https://linux-apps.com/p/998057">linux-apps.com/p/998057</a></td><td></td></tr></tbody></table> <h2 id="creators">Creators</h2> <p>Microsoft's HTML Help Workshop generates CHM files by instructions stored in a HTML Help project file, which bears a .HHP <a href="/facts/File_name_extension/cJgfAym4">file name extension</a> and is a specialized form of <a href="/facts/INI_file/3QR1Etqo">INI file</a>.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p><p><a href="/facts/Lazarus_(IDE)/6Il32HeV">Lazarus</a> and <a href="/facts/Free_Pascal/kmGChqAg">Free Pascal</a> provide a <a href="/facts/Doxygen/Uw1w2lNh">doxygen</a>-like tool for CHM generation and a separate <a href="/facts/Command-line/R9JpGmXQ">command-line</a> compiler called chmcmd. </p> <h2 id="other-utilities">Other utilities</h2> <p>The official viewer in Microsoft Windows (hh.exe) can decompile a CHM file. So can Microsoft HTML Help Workshop and <a href="/facts/7-Zip/0Y8ItlHs">7-Zip</a>. <a href="/facts/Calibre_(software)/HHFeh7Lf">Calibre</a> and <a href="https://github.com/dottedmag/arCHMage">arCHMage</a> can convert CHM into another format. </p> <h2 id="see-also">See also</h2> The Wikibook <i>Windows Programming</i> has a page on the topic of: <i>Compiled HTML Help</i> <ul><li><a href="/facts/WinHelp/qf1N6Sxu">WinHelp</a></li> <li><a href="/facts/Microsoft_Help_2/65kqKm6n">Microsoft Help 2</a></li> <li><a href="/facts/Comparison_of_documentation_generators/xLydRU5z">Comparison of documentation generators</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://msdn2.microsoft.com/en-us/library/bb267846.aspx">HTML Help Web Page on MSDN</a>[<i>dead link</i>]</li> <li><a href="http://msdn2.microsoft.com/en-us/library/bb165722(VS.80).aspx">Microsoft Help 2 Reference</a>[<i>dead link</i>]} (part of Visual Studio SDK for VS7.1 and VS8.0)</li> <li><a href="https://web.archive.org/web/20060718005033/http://www.helpware.net/htmlhelp/hh_info.htm">History of HTML Help</a></li> <li><a href="http://www.nongnu.org/chmspec/latest/index.html">Unofficial (Preliminary) HTML Help Specification</a> (the linked ITSF specification has been moved to <a href="http://www.russotto.net/chm/chmformat.html">the Russotto.net domain</a>)</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Microsoft Security Bulletin MS02-055 - Critical". docs.microsoft.com. Retrieved 2020-10-29. <a href="https://docs.microsoft.com/en-us/security-updates/securitybulletins/2002/ms02-055" target="_blank">https://docs.microsoft.com/en-us/security-updates/securitybulletins/2002/ms02-055</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Full Disclosure: HtmlHelp - .CHM File Heap Overflow". seclists.org. Retrieved 2020-10-29. <a href="https://seclists.org/fulldisclosure/2004/Jul/679" target="_blank">https://seclists.org/fulldisclosure/2004/Jul/679</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"[SOLVED] Windows 10 CHM Help Files showing up blank. - Spiceworks". community.spiceworks.com. Retrieved 2020-10-29. <a href="https://community.spiceworks.com/topic/1961503-solved-windows-10-chm-help-files-showing-up-blank" target="_blank">https://community.spiceworks.com/topic/1961503-solved-windows-10-chm-help-files-showing-up-blank</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Microsoft HTML Help Downloads". Microsoft. Retrieved 6 March 2012. <a href="http://msdn.microsoft.com/en-us/library/ms669985" target="_blank">http://msdn.microsoft.com/en-us/library/ms669985</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Wise, Paul; Wing, Jed (2005). "Unofficial (Preliminary) HTML Help Specification". Retrieved 15 August 2012. <a href="http://www.nongnu.org/chmspec/latest/index.html" target="_blank">http://www.nongnu.org/chmspec/latest/index.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Palade, Alexandru (2005). "Archive::Chm". Retrieved 22 July 2014. <a href="https://metacpan.org/pod/Archive::Chm" target="_blank">https://metacpan.org/pod/Archive::Chm</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Virus Bulletin :: Chamber of horrors". www.virusbulletin.com. Retrieved 2022-01-05. <a href="https://www.virusbulletin.com/virusbulletin/2006/10/chamber-horrors/" target="_blank">https://www.virusbulletin.com/virusbulletin/2006/10/chamber-horrors/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"INFO: Limited Unicode Support in HTML Help". Microsoft. 11 April 2001. Archived from the original on 13 March 2016. Retrieved 17 March 2012. <a href="https://web.archive.org/web/20160313203857/https://support.microsoft.com/en-us/kb/269766/" target="_blank">https://web.archive.org/web/20160313203857/https://support.microsoft.com/en-us/kb/269766/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Salomon, David; Motta, Giovanni; Bryant, David (CON) (2009). Handbook of Data Compression (5th, illustrated ed.). Springer. ISBN 978-1-84882-902-2. <a href="978-1-84882-902-2" target="_blank">978-1-84882-902-2</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Wise, Paul; Wing, Jed (2005). "Unofficial (Preliminary) HTML Help Specification INI formats". Retrieved 1 February 2018. <a href="http://chmspec.nongnu.org/latest/INI.html#HHP" target="_blank">http://chmspec.nongnu.org/latest/INI.html#HHP</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> </ol>