What is CHM? CHM, short name for Compiled HTML Help, is used as the file extension for Compiled HTML Help files. .CHM files are binary files that can be opened by Compiled HTML Help or Compiled HTML Help software. See the sample .CHM file included below.

File Extension: .CHM

MIME Type: application/vnd.ms-htmlhelp

File Content: Compiled HTML Help

.CHM files are Compiled HTML Help files saved as binary files. Here are the first 128 bytes of a sample .CHM file, AMHelp.chm, dumped in HEX values:

49 54 53 46 03 00 00 00 60 00 00 00 01 00 00 00 ITSF............
01 ad 2f e6 09 04 00 00 10 fd 01 7c aa 7b d0 11 ................
9e 0c 00 a0 c9 22 e6 ec 11 fd 01 7c aa 7b d0 11 ................
9e 0c 00 a0 c9 22 e6 ec 60 00 00 00 00 00 00 00 ................
18 00 00 00 00 00 00 00 78 00 00 00 00 00 00 00 ........x.......
54 10 00 00 00 00 00 00 cc 10 00 00 00 00 00 00 T...............
fe 01 00 00 00 00 00 00 c0 fe 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 49 54 53 50 01 00 00 00 ........ITSP....

.CHM files are also archive files that can be opened by 7-Zip. Here is the list of contents in the sample .CHM file, AMHelp.chm:

         4,096 #IDXHDR
             0 #ITBITS
         1,214 #STRINGS
         4,268 #SYSTEM
           400 #TOPICS
           666 #URLSTR
           300 #URLTBL
           400 #WINDOWS
        27,925 $FIftiMain
         2,751 $OBJINST
<DIR>          $WWAssociativeLinks
<DIR>          $WWKeywordLinks
         2,338 allowed_list.htm
         1,930 alttext.xml
         4,701 amhelp.hhc
         1,523 clear_history.htm
           654 compile_date.htm
        11,255 coUA.css
         2,052 coUAprint.css
         1,325 EULA.htm
         2,758 group_policy.htm
         1,847 how_to_tell_infections.htm
         3,428 join_spynet.htm
           123 note.gif
         1,092 Privacy_Policy.htm
         5,487 scan_for_spyware.htm
         3,203 schedule_scans.htm
         1,840 send_to_spynet.htm
        72,959 shared.js
         4,331 spyware_faq.htm
         2,159 SWE_def.htm
         2,355 Turn_av_or_as_onOff.htm
         2,102 Turn_RTP_onOFF.htm
         1,756 Turn_WAS_onOff.htm
         3,400 understand_alerts.htm
         6,674 understand_RTP.htm
         1,528 understand_smart_clean.htm
         2,924 update_definitions.htm
         3,480 using_swe.htm
         4,568 Using_WAS.htm
         3,551 view_restore_items.htm
         1,928 view_scan_progress.htm
            98 warning.gif

.CHM Compiled HTML Help file sample: Click sample.chm to download.

.CHM Compiled HTML Help files can be created and modified by these software:

• 7-Zip - Opens and extracts .CHM files.
• Microsoft Windows - Opens and displays .CHM files.
• Microsoft HTML Help 1.4 - Creates .CHM files.