It's a mangy bear.
Why do I say that and not agree with the Bigfoot "experts" in saying that it's an "unclassified primate"?
1) Bear spines curve like that, primate backs do not. They are straight. And even when bending over, a primate's back does not curve that much.
2) Bear front and back legs are pretty much the same length, ground primates, like chimps and gorillas, have shorter back legs.
3) Bears are common to Pennsylvania, primates are not. In fact, there is no physical evidence, either contemporary or in the fossil record, that primates have ever lived in Pennsylvania since they first evolved some 34 million years ago.
4) Two bear cubs were photographed by the same camera at the same location 28 minutes earlier. This close association suggests that the mystery animal is not only also a bear but a bear related to the cubs. Perhaps even the bear's mother.
The PA Game Commission agrees in saying that it's a bear. The Bigfoot Field Researcher's Organization debunks the Game Commission's statement by saying that the PGC is wrong when they say there are no mountain lions in Pennsylvania when there actually are. First off, this is not a "debunking", this is an ad hominem argument, saying that someone is wrong about one line of reasoning because they are wrong about a completely different thing.
Taken on it's own merits, the arguments of the Bigfoot enthusiasts simply aren't convincing or even compelling. And that they label the photographs "unclassified primate" instead of "unknown animal" lead me to think that they have already made up their minds as to what they want the creature to be.
That is bad science.