Does PDFNet support PHP7?

At the time of this post, no.

PDFNet does not provide pre-built PHP bindings, due to the variety of different (incompatible) versions being used.

We do provide the full steps for customers to generate their own PHP bindings, using SWIG.
https://github.com/PDFTron/PDFNetWrappers

http://www.swig.org/

Unfortunately, at this time SWIG cannot generate PHP7 wrapper.
https://github.com/swig/swig/issues/571

Great news. Latest version of SWIG, 3.0.11, was released and it now supports PHP7

https://sourceforge.net/p/swig/news/2016/12/swig-3011-released/

http://swig.org/