I've heard the claim, mainly from Fundamentalists but also from some Lutherans, that the Pope is an antichrist. Are there any Protestant denominations that specifically teach this, whether it be in their sermons or in their church documents?
Answering from an American Reformed perspective:
The Westminster Confession of Faith (along with its accompanying Larger and Shorter Catechisms) is, to varying degrees, the "official" summary of doctrine for most confessional Reformed churches of English heritage. In its original 1646 form, this document refers to the pope as the anti-Christ in chapter 25, paragraph 6.
The WCF has been adopted as an official doctrinal standard by numerous Reformed denominations, and has been subjected to revisions. Most of these revisions are fairly minor - for instance, owing to differences over preferred forms of government, American Presbyterian churches revised the WCF's teaching on the civil magistrate fairly early in American history.
The clause labelling the pope as anti-christ was removed as part of a revision project undertaken by the northern branch of the mainline Presbyterian Church in America in 1903. Although many of the changes implemented to the WCF at that time have been since rejected by more conservative Presbyterian denominations, Reformed churches at least in America have shown broad acceptance of this particular change.
Part of the reason for this shift has to do with questions over what exactly the Bible means in its talk of an antichrist. Nowadays it seems more common to emphasize 1 John's reference to multiple antichrists, along with a more "spiritualized" conception of antichrist as referring to a set of traits and behaviors rather than a specific temporally and spatially defined historical figure (or even a specific office). Another component is the shift in relations between Protestants and Catholics. The fading temporal and military power of the pope and Catholicism, the decreased religious fervor of most political entities and Europe, and the move toward ecumenicism on both sides since the 1960s (fostered by Vatican II on the Catholic side and the rise of "broad evangelicalism" on the Protestant side) have made it more difficult to convincingly argue that the pope is the man of perdition referred to in Scripture. The belief had more plausibility in the early days of the Reformation, when Protestants saw the pope as the one man totally committed to hunting them down and exterminating them.
In short, in the American Reformed church, few denominations today believe that the pope is the anti-Christ. Undoubtedly some particular churches and individuals may hold to this belief, but to the best of my knowledge that is not terribly common except in really hard-line or "originalist" segments of American Reformed Protestantism. It might be more common to meet someone who considers the pope an anti-Christ - a claim that has a bit more plausibility (from a Protestant perspective) when one emphasizes official Catholic teaching (particularly pre-V2) over actual Catholic practice.
This is my perspective as an American Reformed Christian who stands somewhere between hard-line originalism and broad evangelicalism. I don't know enough about Reformed churches in the UK, or about churches in the US and Europe that have a Dutch Reformed heritage. (Those churches have their own set of standards - the Three Forms of Unity - with which I am less familiar, though I don't think they contain a clause identifying the pope as Anti-Christ.)
Regarding Lutheranism, I also can't speak to that, since I'm not Lutheran. Luther, in his three treatises of 1520, has some really strong words for the pope, and may come close to referring to him as anti-Christ; it's been a while since I've read those works. However, whether such sentiments are contained in the "official" 1577 standards of the Lutheran churches, and how any such sentiments have been handled by different strands of Lutheranism down to the present day: someone else would have to weigh in there.
Below are some articles I would commend to you for further reading if you are so interested - all from the American Reformed perspective that has shaped this particular answer. I hope others will be able to offer input on how this doctrine has been handled in other parts of Christendom.
Almost all Protestant denominations have a historic connection to this claim. The founders of the Lutheran church, Presbyterian churches, and Baptist churches all held this to be the case and it is reflected in the historic confessions like the Westminster confession of faith or the London Baptist Confession of 1689. These churches in the modern day really do not promote the claim any longer and it tends to be viewed as unenlightened and embarrasing.
The only notable Protestant church I know of which actively promotes this view is the Seventh-Day Adventist Church. It is a prominent feature of their views on prophecy and eschatology, which are regularly presented in the current day in prophecy seminars and Bible studies. All other denominations, it seems, have distanced themselves from the roots of their Protestantism.
SDA presentation on the Antichrist: https://youtu.be/xHADyL0enNk
Here is a common reasoning for the pope as an anti christ. It could also apply to bishops or other leaders.
My faith teaches that we are saved by grace alone, justified by faith, and the only source of authority is holy scripture. All believers are priests with the same access to God.
When a person claims infallible authority to rule on spiritual matters, they place themselves in opposition to or above the bible and the teachings of Christ. Therefore they are anti Christs.