"we have prepared" is correct and can be used in written English. It can be used to indicate that someone has taken action to be ready for something. For example: "We have prepared a plan of action for the upcoming meeting."
We have prepared information sheets, listed below, to assist you with the preparation of your laboratory submissions.
We have prepared well.
"We have prepared as best we can.
"We have prepared nothing," he said.
By contrast we have prepared very carefully.
We have prepared and characterized several trithienylbenzenes.
We have prepared the family as best we can.
We have prepared reports on three very attractive steel stocks".
"We have prepared ourselves to deal with that.
"We have prepared 300 V.I.P. gift packs," he added.
We have prepared a website for suppliers and managers.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union