I got it solved this way:
Downloaded latest http://www.pdflib.com/binaries/PDFlib/705/PDFlib-Lite-7.0.5p3.tar.gz
# cd /home/xxx/Downloads/
# wget http://www.pdflib.com/binaries/PDFlib/705/PDFlib-Lite-7.0.5p3.tar.gz
Un-tar-gzip it
# tar xzf PDFlib-Lite-7.0.5p3.tar.gz
# cd PDFlib-Lite-7.0.5p3
See, if and where it contains pdflib.h
# find . -name 'pdflib.h'
./PDFlib-Lite-7.0.5p3/libs/pdflib/pdflib.h
Install via pecl
# pecl install pdflib
If it asks for path, enter the same full path
/home/xxx/Downloads/pdf/PDFlib-Lite-7.0.5p3/libs/pdflib
See from installation messages, if and where it added file pdf.so (in php extensions directory, this dir name may vary but file pdf.so has to exist):
# ls -la /usr/lib/php5/20090626
change pdf.ini
# nano /etc/php5/apache2/php.ini
adding at the end
extension=pdf.so
(You may want to add it in command line php conf /etc/php5/cli/php.ini too)
reload apache
# service apache2 reload
See, if this extension appears
enter at prompt
# php -i |grep PDF
PDFlib
PDFlib Support => enabled
PDFlib GmbH Binary-Version => 7.0.5p3
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