file upload

1) Add this snippet to functions.php

// =========================================================================
// CUSTOMIZER PDF UPLOAD
// =========================================================================
function pdf_customize_register( $wp_customize ) {
 
    // Add Settings
    $wp_customize->add_setting('customizer_setting_pdf', array(
        'transport'         => 'refresh'
    ));
 
    // Add Section
    $wp_customize->add_section('pdf_section', array(
        'title'             => __('PDF', 'name-theme'), 
        'priority'          => 70,
    ));    
 
    // Add Controls
    $wp_customize->add_control( new WP_Customize_Upload_Control( $wp_customize, 'customizer_setting_pdf', array(
        'label'             => __('PDF Upload', 'name-theme'),
        'section'           => 'pdf_section',
        'settings'          => 'customizer_setting_pdf',    
    )));
}
add_action('customize_register', 'pdf_customize_register');

2) Displaying in the Front End

<a href="<?php echo esc_url( get_theme_mod( 'customizer_setting_pdf' ) ); ?>">Download PDF</a>