The most common problem with linking PSPDFKit are missing frameworks. Make sure to either use the provided configuration files or add all frameworks listed in Integrating PSPDFKit manually.
If you see an error like this:
libxml2 is missing. Other similar looking linker errors will indicate other missing frameworks.
If there are syntax errors or compiler errors in the header, this is usually an indication that either Xcode is too old or you are using an unsupported/old SDK (e.g. by copying SDK 7 into Xcode 6; which somewhat works but is neither supported by Apple nor by us)