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How to open .CMP files on Windows

To open .CMP files on Windows, determine the .CMP subtype: ask the sender what created it, or note the product/workflow it came from (for example a “CustomMenu” file tied to application/vnd.yellowriver-custom-menu).

Step-by-step instructions

  1. Determine the .CMP subtype: ask the sender what created it, or note the product/workflow it came from (for example a “CustomMenu” file tied to application/vnd.yellowriver-custom-menu).
  2. Right-click the file → Properties → check the file size and origin; then use Open with… and choose the same application that created or expects this .CMP file (often it is imported via that app’s File → Open/Import menu).
  3. If you still don’t know the producer, try opening a copy in a plain text editor only to see if it contains readable identifiers; if it looks like binary/garbled text, stop and get the correct application rather than trial-and-error.

Alternative methods

  • Open .CMP in a browser-based viewer if desktop apps fail.
  • Try opening .CMP on Windows with a secondary app to rule out app-specific issues.
  • Convert .CMP only with trusted tools when direct opening is not possible.

Common issues

The file won’t open or shows as an unknown format

Because .CMP is used by multiple unrelated formats, the OS may not know which program to use, or you may be trying the wrong application for that subtype.

  1. Ask the sender or check the source system/software to identify what generated the .CMP file.
  2. Open or import it from within that same application (or its companion tools) instead of relying on double-click.
  3. If it is part of a MIME-typed workflow, confirm whether it is intended as a “CustomMenu” file associated with application/vnd.yellowriver-custom-menu.

Opened in the wrong app (garbled text or meaningless output)

Many .CMP files are not plain text; opening binary data in a text editor or the wrong program will look corrupted even if the file is fine.

  1. Stop editing/saving the file after opening it in the wrong program (to avoid overwriting).
  2. Re-open a fresh copy using the application/workflow that created the file (or expects that subtype).

File type association keeps choosing the wrong program

Once you associate .CMP with an app, your OS may repeatedly open it with that app even when future .CMP files are a different subtype.

  1. On Windows, use Open with… → Choose another app for just this file; avoid setting a global default unless all your .CMP files come from the same source.
  2. Prefer opening via the producing application’s File → Open/Import to bypass incorrect OS-level associations.

Security note

.CMP is an ambiguous extension, so treat it as untrusted until you know which application created it; opening it in the wrong tool can trigger parser bugs or unexpected behavior.

Back to .CMP extension page