If you are not sure of your rights/obligations based on reviewing that, I would recommend having a lawyer that specializes in software licensing review it.
It is unlikely anyone on this mailing list will be able to give you more advice about licensing then that, since a) they don't know your specific use case, b) they are not a lawyer and/or c) they do not want to become legally responsible by providing you with legal advice.
From a development point of view, if you are going to be using PDFium I would recommend building it yourself if possible, unless you know/trust the source of pre-built binaries that you listed. I recommend this for 3 reasons: a) it will be easier to debug problems with library usage, b) you are not dependent on a third party for timely updates, and c) you will be able to audit/trust the integrity of the library.
-Ryan Harrison