ms-user.ldf

LDIF directory data file Reference

An .ldf file contains directory data in the LDAP Data Interchange Format, LDIF. The ldifde tool on Windows imports and exports these files. Schema extensions for Active Directory ship as .ldf files, and each record adds, changes, or removes a directory object. Windows also ships .ldf schema files for its lightweight directory service. SQL Server uses the same extension for its transaction log files, which are a different format.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.