"I have informed" is a correct and usable phrase in written English. You can use it any time you want to express that you have communicated information to someone else. For example: "I have informed the IT department about the problem with the network.".
I have informed the management of this decision.
And I have informed Senator Daschle, also, of my decision.
I have informed President Bush, Vice President Cheney and Senator Lott of my decision.
I have informed the district about the problem but there is no action yet".
"I've informed the White House," he said.
"Now it's time for all Thai people to help each other, so I've informed (the host) that I would not go," Prime Minister Yingluck Shinawatra said.
In my subsequent correspondence RIAS said the initial "error" was because they hadn't registered the fact that I had informed them I was now retired.
Awesome tool! I started using it one year ago and I never had to look for another app
Ha Thuy Vy
MA of Applied Linguistic, Maquarie University, Australia