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This document gives you a working example of how to use Secondary File filters.
MSI File Example
If you want to elevate .msi files that are in a network share, you cannot use a commandline filter because the following syntax does not work:
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For an example of a Secondary File filter for use with msiexec and a file share containing msi files to be elvated, go to MSI Files not elevated by Network Share Elevation PolicyElevate MSI files on the network share and see the alternative solution.