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How to open .CAT files on Windows

To open .CAT files on Windows, if you installed the Windows SDK, open Command Prompt and use SignTool to verify the catalog’s signature (for example, the verification command used in Windows driver signing workflows).

Step-by-step instructions

  1. If you installed the Windows SDK, open Command Prompt and use SignTool to verify the catalog’s signature (for example, the verification command used in Windows driver signing workflows).
  2. If the .CAT came with a driver package, keep it with the rest of the package files and let Windows/driver installation validate it; don’t rename it or try to “open” it in an editor.

Alternative methods

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

Common issues

Windows asks what app to use / file won’t open

.CAT files are not general-purpose documents; most systems do not have a default viewer. They are intended for security verification workflows (especially for drivers).

  1. On Windows, use Windows signing/verification tools (for example, SignTool as referenced in Windows driver signing documentation) rather than trying to open it in a document app.
  2. If the file came with a driver or installer, keep it in the same folder as the rest of the package so Windows can validate it during installation.

Catalog signature verification fails

Verification can fail if the catalog was modified, is incomplete, or is not the correct catalog for the files it is supposed to cover; it can also fail if it is unsigned or signed in a way your system does not trust.

  1. Re-download or re-extract the driver/package to ensure the .CAT and related files are intact and unmodified.
  2. Confirm you are verifying the correct .CAT for the associated files (catalogs are typically specific to a file set).

Wrong file type: .CAT is not a Windows security catalog

The .cat extension can be used by different products, but the most common meaning in Windows contexts is a security catalog. If it did not come from a Windows/driver/security workflow, it may be something else.

  1. Check where the file came from (for example, inside a Windows driver package strongly suggests a security catalog).
  2. If it did not come from a Windows security context, ask the sender or source application what created it before attempting to process it.

Security note

.CAT files are security-related metadata used for integrity/signature validation; if a catalog is missing, mismatched, or replaced, it may indicate a tampered or improperly packaged driver/software set.

Back to .CAT extension page