error message

[meichuanneiku]

add in .pro:
INCLUDEPATH += /opt/mupdf-qt/include
LIBS += /opt/mupdf-qt/lib/libmupdf-qt.a
but get Error：
mypdf.o: In function MyPdf::openDocument()': /root/QtExample/build-mupdfTest-Desktop_Qt_5_7_0_GCC_64bit-Debug/../mupdfTest/mypdf.cpp:45: undefined reference toMuPDF::Page::~Page()'
/root/QtExample/build-mupdfTest-Desktop_Qt_5_7_0_GCC_64bit-Debug/../mupdfTest/mypdf.cpp:50: undefined reference to MuPDF::Document::~Document()' /root/QtExample/build-mupdfTest-Desktop_Qt_5_7_0_GCC_64bit-Debug/../mupdfTest/mypdf.cpp:53: undefined reference toMuPDF::loadDocument(QString const&)'
/root/QtExample/build-mupdfTest-Desktop_Qt_5_7_0_GCC_64bit-Debug/../mupdfTest/mypdf.cpp:58: undefined reference to MuPDF::Document::needsPassword() const' /root/QtExample/build-mupdfTest-Desktop_Qt_5_7_0_GCC_64bit-Debug/../mupdfTest/mypdf.cpp:66: undefined reference toMuPDF::Document::authPassword(QString const&)'
/root/QtExample/build-mupdfTest-Desktop_Qt_5_7_0_GCC_64bit-Debug/../mupdfTest/mypdf.cpp:69: undefined reference to MuPDF::Document::title() const' /root/QtExample/build-mupdfTest-Desktop_Qt_5_7_0_GCC_64bit-Debug/../mupdfTest/mypdf.cpp:70: undefined reference toMuPDF::Document::numPages() const'
collect2: error: ld returned 1 exit status
make: *** [mupdfTest] Error 1

That's why？how could this be resolved？

[meichuanneiku]

centos6.5+ Qt 5.7.0 (GCC 4.9.1 20140922 (Red Hat 4.9.1-10), 64 bit)