I don't have the technical knowledge necessary to verify this claim, but various online conversations on Y Combinator indicate that there's an upper limit to the size of a PDF file. This is not because the files themselves have size limits but because Adobe Acrobat itself cannot process files above a certain size, thus capping PDF pages at 381 kilometers by 381 kilometers.
The above image was made by Wikimedia user Alexkr2. It's notable that this file is itself an .SVG or "scalable vector graphic" file. So unlike a PDF file, the map itself has no maximum size.
-via Terrible Maps
