Create a PDF file from a plugin.

admin.php

<?php

add_action( 'save_post', 'bp_generate_pdf', 10, 2 );

public function bp_generate_pdf( $post_id, $post ) {
    // check autosave and permissions.
    
    $should_generate_pdf = $_POST['generatepdf'] ?? 0;

    if ( $should_generate_pdf ) {
        $prev_attach_id = get_post_meta( $post_id, 'pdf_attachment_id', true );

        if ( $prev_attach_id > 0 ) {
            bp_delete_attachments( $post_id );
        }

        // Generate PDF file and returns the attachment ID.
        $attach_id = generate_pdf( $post_id );

        // PDF URL.
        $src = wp_get_attachment_url( $attach_id );

        update_post_meta($post_id, 'pdf_attachment_id', $attach_id);
        update_post_meta($post_id, 'pdf_src', $src);
    }
}

function generate_pdf( $post_id ) {
	// This is the name of your pdf template.
    $source_file = 'PDF-Form';
    $filename    = sprintf( '%s-%d.pdf', $source_file, $post_id );
	
	// Data.
    $form_data = [];
    $data      = get_post_meta( $post_id );

    // Convert metadata to a simple array.
    foreach ( $data as $key => $value ) {
        $form_data[ $key ] = $value[0];
    }

	// Please define your PLUGIN_PATH and make sure the pdf file exists.
    $pdf_data = array(
        'filename'      => $filename,
        'template_path' => PLUGIN_PATH . 'public/assets/' . $source_file . '.pdf',
        'output_path'   => PLUGIN_PATH . $filename
    );

    BP_PDF::create_document( $pdf_data, $form_data );

    return BP_PDF::attach_to_object( $post_id, $pdf_data );
}

function bp_delete_attachments( $post_id ) {
    // Attachments.
    $attachments = get_children([
        'post_parent'   => $post_id,
        'post_type'     => 'any',
        'post_per_page' => -1,
        'post_status'   => 'any'
    ]);

    // Validate.
    if ( is_array( $attachments ) && sizeof( $attachments ) > 0 ) {
        // Delete attachments.
        foreach ( $attachments as $item ) {
            wp_delete_attachment( $item->ID, true );
        }
    }
}