PDFNet building for PHP error on Linux


I'm trying building the PDFNetPHP in a Linux Debian 64bits. I follow the instructions on https://github.com/PDFTron/PDFNetWrappers but I get this error with the cmake:

$ cmake -D BUILD_PDFNetPHP=ON ..
-- The CXX compiler identification is GNU 4.9.2
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Found SWIG: /usr/bin/swig2.0 (found version "2.0.12")
-- Using SWIG 2.0.12
CMake Error at PDFNetPHP/CMakeLists.txt:35 (message):
  An error has occurred while getting PHP include directories. Error:

-- Configuring incomplete, errors occurred!

What I'm doing wrong? c++ installed and running, swig installed and running, cmake installed and running...

You will need to install the PHP headers. On a Debian or Ubuntu environment you can run something like

apt-get install php5-dev