[venkatasu]

Thank you Anglika for your kind information and useful links.

I find it easy to understand the usage of 'had' for past perfect tense in sentences quoted by you. It's great. But I find it very hard to spot the usage of 'had' (for past perfect tense) in passage comprising few lines.
For example I spot a past perfect tense usage in a sentence for which I find it difficult to find the relative past action.

I would be much obliged if you help me in this regard.

Thank you in advance.