Class not found trying to integrate TCPDF

You are copying code you don't understand and you get an error. And these are the basics of PHP.

PHP Code:

use App\ThirdParty\TCPDF\Tcpdf; 


This line is trying to import the class and

1. The class file must be reachable through the path App/ThirdParty/TCPDF/Tcpdf.php
2. The class must be in the specified namespace (App\ThirdParty\TCPDF).

If you haven't guessed yet, then the shared library will not have the App\ThirdParty\TCPDF namespace.
That's why you get your error.

There are 2 simple solutions.

CodeIgniter way

1. Unpack the library from github to ThirdParty/TCPDF
2. Change config App/Config/Autoload. 
Add the line to the $classmap property

PHP Code:

public $classmap = [
     'TCPDF' => APPPATH . '/ThirdParty/TCPDF/tcpdf.php',
    ]; 


3. Import the library into your controller.

PHP Code:

<?php 
namespace Your\Controller\Namespace
use TCPDF;  


Now you can create an instance of the class.

The easy way

1.Install the library with composer

Code:

composer require tecnickcom/tcpdf

2. Import the library into your controller.

PHP Code:

<?php 
namespace Your\Controller\Namespace
use TCPDF;