Converting PDF to text in PHP: How do I resolve “Call to undefined function PDFNet_Initialize()"

Q: I want to know there are any example for converting PDF to text in
php. I have downloaded trial version of PDFNet but it gives error
“Call to undefined function PDFNet_Initialize() in /home/content/n/e/w/
newgensandbox/html/newgensoft/PDFNetC64/Lib/PDFNetPHP.php on line
15826”. At this line it requires License key how can I get license
key for trial version.
A: The trial version of PDFNet (including bindings for C/C++/Java/PHP/
Python/Ruby/Objective-C) does not require any license keys. The
license key argument for the Initialize method is optional. It seems
that you are experiencing these errors because you missed a step in
setting up your PHP interpreter with PDFNet.

You will need to add the (or php_PDFNetTS.dll in Windows)
as one of your PHP extensions. In Linux systems, you may need to put
the in an accessible directory to PHP because of file
permissions. You will also need to make sure that (or
PDFNetC.dll) is placed on the correct directories (/usr/lib or %WINDIR%
\System32). You should be able see all these information in
PHP_README.txt included in the PDFNetC packages.