I spent the first 47 years of my life as an Evangelical Protestant.
They would say that they aren’t against His Church. They would say that they are members of the invisible universal (or catholic) church of Jesus Christ, which has existed since the time of the apostles, and will continue through all eternity.
And they would show you all the Bible verses that prove it.
And then they would hand YOU that Bible and ask you to show them in the Bible where Jesus established an actual “church organization.”
Can you answer them?

Can you open that Bible (which does NOT Have the tabs on the pages to show you where the books are!) and point to those passages and verses that demonstrate that Jesus DID establish an actual church organization? Can you do this without using any extra-Biblical historical writings?
Here’s the deal, folks. When you are talking to Evangelical Protestants, history means nothing, at least at first. They are only concerned with what the Bible says, so you have to use the Bible alone. And this is easy enough to do with the question of the Church that Jesus Christ established.
Once you’ve demonstrated something from the Bible, then you can turn to history. If I were you, I would point your Protestant friend to the resources at Calvin College in Grand Rapids, Michigan . This Protestant college has the complete works of all the early church fathers (it’s online, too!). Your Protestant friend is more likely to trust Calvin than the Vatican.
Protestants may be able to misinterpret the Bible, but they can’t get around the historical writings, other than to claim that they are ALL spurious. But then they learn that the authors of many of those writings were actual students of the apostles, and that most of these early church fathers underwent cruel martyrdom for their faith–again, it’s hard to get around this and accuse people of corrupting “true Christianity” and starting up “Catholicism.” Martyrs truly do bear witness to Jesus Christ, don’t they?
Anyway, my best advice to those of you who are attempting to witness to Protestants is “don’t underestimate them.” I think a LOT of Catholics think that Protestants are just ignorant, and only know a few Bible verses–and then when the Catholic starts actually talking with the Protestant, they learn, to their dismay, that the Protestant has a huge body of scholarship and theology behind their beliefs, and what often happens is that the CATHOLIC is the one who ends up converting to Protestantism. DO NOT UNDERESTIMATE the scholarship of your Protestant friends.
And the other piece of advice I can give you is LOVE LOVE LOVE! One of the main reasons I converted to Catholicism is the practical and compelling love of many Catholics that I had known over the years. Sometimes I hear Catholics say that they just can’t be around certain Protestants anymore and they’re going to stay away from them. Please don’t do this. Stick with them. Never stop loving them. You will know in heaven how much good your love did for them!