This is an excerpt from a newspaper.
In September 2014 the Delhi high court had restrained the institute from using words like......
Why are we using "had" here.. Can we use past indefinite?
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The past perfect is used when there are two different times in the past that are relevant: the time the speaker is focussing on, and the earlier time when the action took place.
The example says that the writer is focussing on a time after September 2014 (but before the present) and talking about some that happened earlier than that time.
It is usually possible to substitute a simple past, but it changes the meaning, in that it does not focus attention on a time in the past the way the past perfect does.