Not sure what you mean by "other CE operating systems can't." Plenty of Pocket PC apps will work on CE 4.x .net, CE 5, and CE 6 devices. Usually they need DLL files compiled for Pocket PCs, though. Adobe Reader, for example, needs the Pocket PC version of mfcce300.dll, as well as its dependencies
(aygshell.dll and doclist.dll
). Not only that, but many apps written for Pocket PCs can even work on H/PC Pro devices
(primarily Visual Basic apps
), and some even work on CE 2.0 devices
(.NET Compact Framework 1.0 apps
). Which version of PocketXpdf are you using? It may be a version for Windows Mobile 2003, which is based on CE 4.2 .net. There are tons of threads on these forums talking about making Pocket PC apps work on H/PCs and core CE devices.