See also Installation for an overview of the portable and installer versions.

SumatraPDF may have told you that you have a corrupted installation.

SumatraPDF comes as a portable version and as an installer.

A portable version is a self-contained executable and cannot be corrupted.

An installer needs to be run to be properly installed. Part of installation is extracting the engine library (libsumatrapdf.dll from 3.7, named libmupdf.dll through 3.6).

The installation is corrupted when:

If you want to place SumatraPDF in any location, under any name, use the self-contained portable version.

If you want to use the installable version, install it. The installer will run if the .exe filename contains -install (as it will if you download an official build).

If you rename the .exe, you can force it to run as the installer with the -install option.

Alternatively, you can extract libsumatrapdf.dll and all other files with the -x option.