That's the gorilla suit used in the 1939 movie
The Gorilla, starring the Ritz Brothers (there's a very good reason why everybody reading this just went: "Who?") and Bela Lugosi at a time when he had to be in films like this because his career was in the meltdown that would culminate in his appearing in Ed Wood movies. In other words, it wasn't exactly a big-budget state-of-the-art special-effects blockbuster, even by the standards of 1939.
But you know what? The suit's really not that bad! On grainy, slightly out-of-focus 16mm shot from quite a long way away, neatly combed and looking nice and glossy in the sunlight, I reckon it would look a lot more convincing than it does in the close-up you see here. And this is the kind of reasonably-priced gorilla suit that Hollywood comedy B-movies starring second-string funny-men and horror has-beens were using nearly 30 years before Patterson & Gimlin shot their 53 seconds of "documentary footage".
You will also observe that the actor (Art Miles, if you're interested - by the way, this particular gorilla is for some reason called Poe) has at least taken the trouble to observe how real apes move; his stance in this picture is much less like a man in a suit that Patty's is in every single frame. Legendary gorilla actors such as George Barrows and Bob Burns spent a lot of time at the zoo watching genuine gorillas. Patterson & Gimlin's ape impersonator, on the other hand, was just the tallest guy they knew, and was most unlikely to have thought about this aspect of his brief performance very much.
Here's the thing. P&G estimated the size of the critter at about 7'6" - the kind of height an average Bigfoot is supposed to attain. However, evidence in the film allowed investigators to determine that the creature was at least a foot shorter than that. In other words, about the height of the tallest man anybody who wasn't a basketball player might be reasonably expected to know. The actor in the suit has obviously been instructed to try and make his footprints as widely separated as possible in order to reinforce the claim that he was even taller than he really was - look at the very unnatural way in which he's walking, like somebody crossing a stream using stepping-stones that are just a little too far apart.