Which is appropriate?

I would write: It is my pleasure to inform you...

It is my pleasure to inform you.

Anonymous I feel great pleasure in informing/to inform you...

Your sentence seems correct grammatically, either with in informing you or to inform you. However, you could also say: It's my great pleasure to inform you or I'm highly pleased to inform you or I'm feeling highly pleased to inform you that ...

Laborious Anonymous I feel great pleasure in informing/to inform you...Your sentence seems correct grammatically, either with in informing you or to inform you. However, you could also say: It's my great pleasure to inform you or I'm highly pleased to inform you or I'm feeling highly pleased to inform you that ... .

Apart from the one I have underlined,

fivejedjonApart from the one I have underlined, none of these is natural in BrE.

Nor in American English.

Thanks, 5jj and Philip, for your responses. But is there any particular reason why you consider them 'unnatural', please? Is it because of the word 'highly' in them? Or Is there something else which makes them 'unnatural' to you?

I'm asking this to you, because in my country I hear both the expressions, I'm pleased to... and I'm feeling pleased to... In a situ

It's simply that we say some things and not others, There is no particular reason for this.

Don't forget that Indian English accepts some structures, collocations and vocabulary items that may be unnatural in BrE and AmE.