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How to open .CHM files on iOS

To open .CHM files on iOS, cHM viewing is not consistently supported natively; if the Files app can’t preview it, share it to a CHM-capable reader app (if available) or open it on a desktop OS.

Step-by-step instructions

  1. CHM viewing is not consistently supported natively; if the Files app can’t preview it, share it to a CHM-capable reader app (if available) or open it on a desktop OS.

Common issues

The .CHM file won’t open (or opens in the wrong app)

File association may be missing or your device may not have a CHM/HTML Help viewer installed.

  1. On Windows/Linux, use “Open with” to select a CHM-capable viewer and set it as the default if desired.
  2. On macOS/mobile, use a CHM viewer app if available; otherwise open the file on Windows where support is most common.

Blank pages, missing navigation/search, or links don’t work

Some viewers have partial CHM feature support, so the TOC, index, or certain internal links/scripts may not behave the same as in the Windows HTML Help viewer.

  1. Try opening the same .CHM file in the Windows HTML Help viewer to confirm whether the file itself is OK.
  2. If you must use another platform, try a different CHM viewer there (feature support varies by application).

Windows shows a security warning or content is blocked

Windows can restrict CHM content (especially when downloaded) which may prevent scripts or some internal content from loading correctly.

  1. Move the .CHM to a local folder (not a network share) and try again.
  2. If you trust the source, use Windows file properties (where available) to unblock, then reopen.

File is corrupted or incomplete

Because CHM is a compiled container, a partial download or truncation can prevent it from opening or cause missing sections.

  1. Re-download or re-copy the file from the original source.
  2. Test the file on another machine/viewer to rule out a device-specific viewer problem.

Security note

CHM files can contain active HTML content; treat CHM files from untrusted sources as potentially risky and avoid opening unknown CHM attachments.

Back to .CHM extension page