Action description – Descriptive text that can be used to identify this particular action in the Actions list.

Target client folder – The folder on the client to place files that contains the file(s) you are adding/replacing.

Subdirectories – The directory below the designated client root folder that contains the files.

Version Information displays the assembly version and file version of the baseline file and the target file.

The Patch Existing File action utilizes the Microsoft Delta Compression API to create a differential patch file between two versions of an assembly during an update build, and then packages the patch file into the update.

As the update is executed, this differential patch is combined with the base file that exists on a deployed client to construct the target file.

Utilizing the Patch Existing File action can significantly reduce the size of the resulting update package.  The specific version of the baseline file must be present on the system being updated.

NOTE: The Windows Installer SDK must be present on the system building the update package.  Get it here.  Patch extraction support is available on Windows 2000 and later.

See File Patching Action for more details