This is a Windows system installed file with Windows File Protection (WFP) enabled.
propsys.dll has 37 known versions, the most recent one is 7.00.7600.16385 (win7_rtm.090713-1255). The average file size is about 243.3 KB.
Microsoft Property System for Windows Search, formerly known as Windows Desktop Search (WDS) is an indexed desktop search platform. Windows Search builds a full-text index of files on a computer. Windows Search features incremental search search. The search service consists of several components, including the Gatherer, the Merger, the Backoff Controller, and the Query Processor, among others.
(Note, the behaviors below are for all versions of propsys.dll, select a unique version for details.)
United States installs about 63.01% of Windows® Search.