There have, in fact, been three occasions on which major "platforms" have been published in the name of Reform Judaism: the Pittsburgh Platform, in 1885; the Columbus Platform, in 1937; and most recently, a statement (more descriptive than prescriptive) called Reform Judaism: A Centenary Perspective, promulgated in 1976. The three make a fascinating study. If you are interested in pursuing this topic in depth, I suggest you read a book called Reform Judaism Today, by Eugene Borowitz. The author was the chair of the committee that developed the Centenary Perspective, and the book is, in essence, an extended commentary on that 2-page platform.
In my opinion, the central dividing point between Reform and Orthodox Judaism is over the question of halacha, that is, Jewish law. The Orthodox believe (in varying degrees and with varying interpretations) that halacha represents an accurate, precise description of what God want us to do. Therefore, the law is binding on us. That's it, plain and simple. No ifs, ands or buts. God is God. We know what God wants. We have to do it. It doesn't matter whether we understand it or not. It doesn't matter whether we like it or not. It doesn't matter whether it gives us a spiritual feeling or not. It doesn't matter whether we feel it enhances our lives or not. God wants it, we have to do it. Period.
The Reform position is much more complicated. First, how do we know what God wants? Reform asserts that every knowledgeable Jew has an equal claim to a personal understanding of what God wants. Therefore, Movement-wide agreement is, in principle, not necessary nor desirable, nor probably even possible. We each (if we are knowledgeable about the tradition, if we confront it seriously and take its claims and its wisdom seriously) have the ability, the freedom, indeed the responsibility to come to a [potentially differing] personal understanding of what God wants us to do.
But if we are free to choose, what, then, is the point of Torah (and halacha)? For me, and I think for many other Reform Jews as well (though in principle it doesn't matter), it is a record of how our people, in widely differing times, places and societal circumstances, experienced God's presence in their lives, and responded. Each aspect of halacha is a possible gateway to experience of the holy, the spiritual. Each aspect worked for some Jews, once upon a time, somewhere in our history. Each, therefore, has the potential to open up holiness for people in our time as well, and for me personally.
However, each does not have equal claim on us, on me. Some (the agricultural laws, for instance) are no longer possible to observe. Others (the sacrificial laws, for instance) come from a social context so foreign to our own that it would be impossible to conceive modern people finding holiness in their revival. Much of the halacha arose in societal settings where distance from the peoples in whose midst we lived was desirable. The "outside" world was dark, dangerous and threatening. That is no longer our situation. We welcome, applaud and are uplifted by much of Western culture. Portions of the halacha whose main purpose seems to be to distance us from our surroundings no longer seem functional.
Yet some parts of the halachic tradition seem perfect correctives to the imbalances of life in modernity. Shabbat, for example, reminds us of the importance of balance as we struggle with time. The various ethical imperatives remind us not to make idols of the self. And so on. In those parts of tradition, we are sometimes blessed to experience a sense of God's closeness. In my personal life, I emphasize those areas. And other areas of halacha, I de-emphasize, or sometimes abandon.
Reform Judaism affirms my right, our right, to make those kinds of choices.
Many Orthodox Jews are offended by our presumption, to give individuals the right to abandon the practice of what, in their opinion, is God's will. And some of them get positively furious when we lead others down those same paths (in their opinion, away from what God wants). And it makes some of them really go bonkers, when we assert that we are making those choices, precisely in the name of Judaism, that is, in the name of getting closer to what we believe will bring us closer to God and to what God calls us to do.