Invoice PDF Generation

Overview

Simple Invoice uses the HTML2PDF library (built on TCPDF) to generate professional PDF invoices with company branding, client information, product line items, and automatic calculations. PDFs are generated on-the-fly when users click the print button.

PDF Libraries

The system uses two PDF libraries:

TCPDF 5.0.002: Low-level PDF generation library located in pdf/_tcpdf_5.0.002/
HTML2PDF: Wrapper library that converts HTML to PDF using TCPDF, located in pdf/html2pdf.class.php

HTML2PDF allows developers to design invoice templates using familiar HTML/CSS, which are then converted to PDF format.

PDF Generation Entry Point

The main PDF generation file is pdf/documentos/factura_pdf.php:

pdf/documentos/factura_pdf.php

session_start();
if (!isset($_SESSION['user_login_status']) AND $_SESSION['user_login_status'] != 1) {
    header("location: ../../login.php");
    exit;
}

// Connect To Database
include("../../config/db.php");
include("../../config/conexion.php");
include("../../funciones.php");

$session_id = session_id();

Validation Check

Before generating the PDF, the system ensures products are in the cart:

pdf/documentos/factura_pdf.php

$sql_count = mysqli_query($con, "SELECT * FROM tmp WHERE session_id='" . $session_id . "'");
$count = mysqli_num_rows($sql_count);

if ($count == 0) {
    echo "<script>alert('No hay productos agregados a la factura')</script>";
    echo "<script>window.close();</script>";
    exit;
}

Invoice Parameters

Invoice data is received via GET parameters:

pdf/documentos/factura_pdf.php

// Variables por GET
$id_cliente = intval($_GET['id_cliente']);
$id_vendedor = intval($_GET['id_vendedor']);
$condiciones = mysqli_real_escape_string($con, (strip_tags($_REQUEST['condiciones'], ENT_QUOTES)));

Invoice Number Generation

The system automatically generates sequential invoice numbers:

pdf/documentos/factura_pdf.php

$sql = mysqli_query($con, 
    "SELECT LAST_INSERT_ID(numero_factura) as last 
     FROM facturas 
     ORDER BY id_factura DESC 
     LIMIT 0, 1");
$rw = mysqli_fetch_array($sql);
$numero_factura = $rw['last'] + 1;

Invoice numbers are auto-incremented from the last invoice in the database.

HTML Template Processing

The PDF content is generated from an HTML template:

pdf/documentos/factura_pdf.php

$simbolo_moneda = get_row('perfil', 'moneda', 'id_perfil', 1);

// Get the HTML
ob_start();
include(dirname('__FILE__') . '/res/factura_html.php');
$content = ob_get_clean();

HTML2PDF Initialization

The HTML content is converted to PDF format:

pdf/documentos/factura_pdf.php

try {
    // Init HTML2PDF
    $html2pdf = new HTML2PDF('P', 'LETTER', 'es', true, 'UTF-8', array(0, 0, 0, 0));
    
    // Display the full page
    $html2pdf->pdf->SetDisplayMode('fullpage');
    
    // Convert
    $html2pdf->writeHTML($content, isset($_GET['vuehtml']));
    
    // Send the PDF
    $html2pdf->Output('Factura.pdf');
} catch(HTML2PDF_exception $e) {
    echo $e;
    exit;
}

PDF Parameters

‘P’: Portrait orientation
‘LETTER’: Letter size paper (8.5” x 11”)
‘es’: Spanish language
true: Unicode support
‘UTF-8’: Character encoding
array(0, 0, 0, 0): Margins (top, right, bottom, left)

Invoice HTML Template

The template in pdf/documentos/res/factura_html.php defines the PDF layout:

Template Styling

pdf/documentos/res/factura_html.php

<style type="text/css">
table { vertical-align: top; }
tr    { vertical-align: top; }
td    { vertical-align: top; }

.midnight-blue {
    background: #2c3e50;
    padding: 4px 4px 4px;
    color: white;
    font-weight: bold;
    font-size: 12px;
}

.silver {
    background: white;
    padding: 3px 4px 3px;
}

.clouds {
    background: #ecf0f1;
    padding: 3px 4px 3px;
}

.border-top { border-top: solid 1px #bdc3c7; }
.border-left { border-left: solid 1px #bdc3c7; }
.border-right { border-right: solid 1px #bdc3c7; }
.border-bottom { border-bottom: solid 1px #bdc3c7; }
</style>

Page Configuration

pdf/documentos/res/factura_html.php

<page backtop="15mm" backbottom="15mm" backleft="15mm" backright="15mm" 
      style="font-size: 12pt; font-family: arial">
    <page_footer>
        <table class="page_footer">
            <tr>
                <td style="width: 50%; text-align: left">
                    Página [[page_cu]]/[[page_nb]]
                </td>
                <td style="width: 50%; text-align: right">
                    &copy; <?php echo "obedalvarado.pw "; echo $anio = date('Y'); ?>
                </td>
            </tr>
        </table>
    </page_footer>

Company Logo Integration

The invoice header includes company branding:

pdf/documentos/res/encabezado_factura.php

<?php include("encabezado_factura.php"); ?>

This file loads company information from the perfil table including:

Company logo
Company name
Address and contact details
Tax information

Client Information Section

pdf/documentos/res/factura_html.php

<table cellspacing="0" style="width: 100%; text-align: left; font-size: 11pt;">
    <tr>
        <td style="width:50%;" class='midnight-blue'>FACTURAR A</td>
    </tr>
    <tr>
        <td style="width:50%;">
            <?php 
            $sql_cliente = mysqli_query($con, "SELECT * FROM clientes WHERE id_cliente='$id_cliente'");
            $rw_cliente = mysqli_fetch_array($sql_cliente);
            echo $rw_cliente['nombre_cliente'];
            echo "<br>";
            echo $rw_cliente['direccion_cliente'];
            echo "<br> Teléfono: ";
            echo $rw_cliente['telefono_cliente'];
            echo "<br> Email: ";
            echo $rw_cliente['email_cliente'];
            ?>
        </td>
    </tr>
</table>

Invoice Metadata

pdf/documentos/res/factura_html.php

<table cellspacing="0" style="width: 100%; text-align: left; font-size: 11pt;">
    <tr>
        <td style="width:35%;" class='midnight-blue'>VENDEDOR</td>
        <td style="width:25%;" class='midnight-blue'>FECHA</td>
        <td style="width:40%;" class='midnight-blue'>FORMA DE PAGO</td>
    </tr>
    <tr>
        <td style="width:35%;">
            <?php 
            $sql_user = mysqli_query($con, "SELECT * FROM users WHERE user_id='$id_vendedor'");
            $rw_user = mysqli_fetch_array($sql_user);
            echo $rw_user['firstname'] . " " . $rw_user['lastname'];
            ?>
        </td>
        <td style="width:25%;"><?php echo date("d/m/Y"); ?></td>
        <td style="width:40%;">
            <?php 
            if ($condiciones == 1) { echo "Efectivo"; }
            elseif ($condiciones == 2) { echo "Cheque"; }
            elseif ($condiciones == 3) { echo "Transferencia bancaria"; }
            elseif ($condiciones == 4) { echo "Crédito"; }
            ?>
        </td>
    </tr>
</table>

Product Line Items Table

pdf/documentos/res/factura_html.php

<table cellspacing="0" style="width: 100%; text-align: left; font-size: 10pt;">
    <tr>
        <th style="width: 10%; text-align:center" class='midnight-blue'>CANT.</th>
        <th style="width: 60%" class='midnight-blue'>DESCRIPCION</th>
        <th style="width: 15%; text-align: right" class='midnight-blue'>PRECIO UNIT.</th>
        <th style="width: 15%; text-align: right" class='midnight-blue'>PRECIO TOTAL</th>
    </tr>

Product Loop

pdf/documentos/res/factura_html.php

<?php
$nums = 1;
$sumador_total = 0;
$sql = mysqli_query($con, 
    "SELECT * FROM products, tmp 
     WHERE products.id_producto = tmp.id_producto 
     AND tmp.session_id = '" . $session_id . "'");

while ($row = mysqli_fetch_array($sql)) {
    $id_tmp = $row["id_tmp"];
    $id_producto = $row["id_producto"];
    $codigo_producto = $row['codigo_producto'];
    $cantidad = $row['cantidad_tmp'];
    $nombre_producto = $row['nombre_producto'];
    $precio_venta = $row['precio_tmp'];
    
    // Format prices
    $precio_venta_f = number_format($precio_venta, 2);
    $precio_venta_r = str_replace(",", "", $precio_venta_f);
    $precio_total = $precio_venta_r * $cantidad;
    $precio_total_f = number_format($precio_total, 2);
    $precio_total_r = str_replace(",", "", $precio_total_f);
    $sumador_total += $precio_total_r;
    
    // Alternate row colors
    $clase = ($nums % 2 == 0) ? "clouds" : "silver";
    ?>
    <tr>
        <td class='<?php echo $clase; ?>' style="width: 10%; text-align: center">
            <?php echo $cantidad; ?>
        </td>
        <td class='<?php echo $clase; ?>' style="width: 60%; text-align: left">
            <?php echo $nombre_producto; ?>
        </td>
        <td class='<?php echo $clase; ?>' style="width: 15%; text-align: right">
            <?php echo $precio_venta_f; ?>
        </td>
        <td class='<?php echo $clase; ?>' style="width: 15%; text-align: right">
            <?php echo $precio_total_f; ?>
        </td>
    </tr>
    <?php 
    // Insert into permanent detail table
    $insert_detail = mysqli_query($con, 
        "INSERT INTO detalle_factura 
         VALUES ('', '$numero_factura', '$id_producto', '$cantidad', '$precio_venta_r')");
    $nums++;
}
?>

Product line items alternate between silver and cloud-colored rows for better readability.

Invoice Totals

pdf/documentos/res/factura_html.php

<?php
$impuesto = get_row('perfil', 'impuesto', 'id_perfil', 1);
$subtotal = number_format($sumador_total, 2, '.', '');
$total_iva = ($subtotal * $impuesto) / 100;
$total_iva = number_format($total_iva, 2, '.', '');
$total_factura = $subtotal + $total_iva;
?>

<tr>
    <td colspan="3" style="width: 85%; text-align: right;">
        SUBTOTAL <?php echo $simbolo_moneda; ?>
    </td>
    <td style="width: 15%; text-align: right;">
        <?php echo number_format($subtotal, 2); ?>
    </td>
</tr>
<tr>
    <td colspan="3" style="width: 85%; text-align: right;">
        IVA (<?php echo $impuesto; ?>)% <?php echo $simbolo_moneda; ?>
    </td>
    <td style="width: 15%; text-align: right;">
        <?php echo number_format($total_iva, 2); ?>
    </td>
</tr>
<tr>
    <td colspan="3" style="width: 85%; text-align: right;">
        TOTAL <?php echo $simbolo_moneda; ?>
    </td>
    <td style="width: 15%; text-align: right;">
        <?php echo number_format($total_factura, 2); ?>
    </td>
</tr>

Finalizing the Invoice

After generating the PDF, the invoice is saved to the database:

pdf/documentos/res/factura_html.php

<?php
$date = date("Y-m-d H:i:s");
$insert = mysqli_query($con, 
    "INSERT INTO facturas 
     VALUES (NULL, '$numero_factura', '$date', '$id_cliente', '$id_vendedor', 
             '$condiciones', '$total_factura', '1')");

// Clear temporary items
$delete = mysqli_query($con, "DELETE FROM tmp WHERE session_id='" . $session_id . "'");
?>

Once the PDF is generated, temporary items are deleted from the tmp table. Do not refresh the PDF generation page as it will create duplicate invoices.

Print Functionality

The print function is triggered from the invoice edit page:

editar_factura.php

<button type="button" class="btn btn-default" onclick="imprimir_factura('<?php echo $id_factura; ?>')">
    <span class="glyphicon glyphicon-print"></span> Imprimir
</button>

The imprimir_factura() function (in js/VentanaCentrada.js) opens a popup window with the PDF.

PDF Features

Company Logo

Displays company logo from profile settings

Client Information

Full client details including address and contact

Product Line Items

Detailed table with quantities, descriptions, and prices

Automatic Calculations

Subtotal, tax, and total computed automatically

Payment Method

Displays selected payment terms on invoice

Professional Styling

Clean, branded design with alternating row colors

PDF Generation Workflow

Add Products

Products are added to the tmp table with the user’s session ID

Click Print

User clicks the print button on the invoice form

Validate Data

System checks that products exist and all required fields are filled

Generate HTML

Invoice template is populated with client, vendor, and product data

Convert to PDF

HTML2PDF converts the HTML template to a PDF document

Save to Database

Invoice header and line items are permanently saved to the database

Clear Session

Temporary items are deleted from the tmp table

Display PDF

PDF is sent to the browser for viewing, download, or printing

pdf/documentos/factura_pdf.php - Main PDF generation entry point
pdf/documentos/res/factura_html.php - Invoice HTML template
pdf/documentos/res/encabezado_factura.php - Company header template
pdf/html2pdf.class.php - HTML to PDF conversion library
pdf/_tcpdf_5.0.002/tcpdf.php - TCPDF core library
js/VentanaCentrada.js - Popup window helper
funciones.php - Helper functions like get_row()

The PDF system uses output buffering (ob_start() and ob_get_clean()) to capture the HTML template output before conversion to PDF.

Get Started

Core Features

Configuration

Deployment

Overview

PDF Libraries

PDF Generation Entry Point

Validation Check

Invoice Parameters

Invoice Number Generation

HTML Template Processing

HTML2PDF Initialization

PDF Parameters

Invoice HTML Template

Template Styling

Page Configuration

Company Logo Integration

Client Information Section

Invoice Metadata

Product Line Items Table

Product Loop

Invoice Totals

Finalizing the Invoice

Print Functionality

PDF Features

Company Logo

Client Information

Product Line Items

Automatic Calculations

Payment Method

Professional Styling

PDF Generation Workflow

Build docs developers (and LLMs) love

Get Started

Core Features

Configuration

Deployment

​Overview

​PDF Libraries

​PDF Generation Entry Point

​Validation Check

​Invoice Parameters

​Invoice Number Generation

​HTML Template Processing

​HTML2PDF Initialization

​PDF Parameters

​Invoice HTML Template

​Template Styling

​Page Configuration

​Company Logo Integration

​Client Information Section

​Invoice Metadata

​Product Line Items Table

​Product Loop

​Invoice Totals

​Finalizing the Invoice

​Print Functionality

​PDF Features

Company Logo

Client Information

Product Line Items

Automatic Calculations

Payment Method

Professional Styling

​PDF Generation Workflow

​Related Files

Build docs developers (and LLMs) love

Overview

PDF Libraries

PDF Generation Entry Point

Validation Check

Invoice Parameters

Invoice Number Generation

HTML Template Processing

HTML2PDF Initialization

PDF Parameters

Invoice HTML Template

Template Styling

Page Configuration

Company Logo Integration

Client Information Section

Invoice Metadata

Product Line Items Table

Product Loop

Invoice Totals

Finalizing the Invoice

Print Functionality

PDF Features

PDF Generation Workflow

Related Files