Crear documentos PDF con PHP

Descargar la librería fpdf:
http://www.fpdf.org/

Crear un fichero llamado tablas_pdf.php:
<?php
class PDF_MySQL_Table extends FPDF
{
var $ProcessingTable=false;
var $aCols=array();
var $TableX;
var $HeaderColor;
var $RowColors;
var $ColorIndex;

function Header()
{
    //Print the table header if necessary
    if($this->ProcessingTable)
        $this->TableHeader();
}

function TableHeader()
{
    $this->SetFont('Arial','B',12);
    $this->SetX($this->TableX);
    $fill=!empty($this->HeaderColor);
    if($fill)
        $this->SetFillColor($this->HeaderColor[0],$this->HeaderColor[1],$this->HeaderColor[2]);
    foreach($this->aCols as $col)
        $this->Cell($col['w'],6,$col['c'],1,0,'C',$fill);
    $this->Ln();
}

function Row($data)
{
    $this->SetX($this->TableX);
    $ci=$this->ColorIndex;
    $fill=!empty($this->RowColors[$ci]);
    if($fill)
        $this->SetFillColor($this->RowColors[$ci][0],$this->RowColors[$ci][1],$this->RowColors[$ci][2]);
    foreach($this->aCols as $col)
        $this->Cell($col['w'],5,$data[$col['f']],1,0,$col['a'],$fill);
    $this->Ln();
    $this->ColorIndex=1-$ci;
}

function CalcWidths($width,$align)
{
    //Compute the widths of the columns
    $TableWidth=0;
    foreach($this->aCols as $i=>$col)
    {
        $w=$col['w'];
        if($w==-1)
            $w=$width/count($this->aCols);
        elseif(substr($w,-1)=='%')
            $w=$w/100*$width;
        $this->aCols[$i]['w']=$w;
        $TableWidth+=$w;
    }
    //Compute the abscissa of the table
    if($align=='C')
        $this->TableX=max(($this->w-$TableWidth)/2,0);
    elseif($align=='R')
        $this->TableX=max($this->w-$this->rMargin-$TableWidth,0);
    else
        $this->TableX=$this->lMargin;
}

function AddCol($field=-1,$width=-1,$caption='',$align='L')
{
    //Add a column to the table
    if($field==-1)
        $field=count($this->aCols);
    $this->aCols[]=array('f'=>$field,'c'=>$caption,'w'=>$width,'a'=>$align);
}

function Table($query,$prop=array())
{
    //Issue query
    $res=mysql_query($query) or die('Error: '.mysql_error()."<BR>Query: $query");
    //Add all columns if none was specified
    if(count($this->aCols)==0)
    {
        $nb=mysql_num_fields($res);
        for($i=0;$i<$nb;$i++)
            $this->AddCol();
    }
    //Retrieve column names when not specified
    foreach($this->aCols as $i=>$col)
    {
        if($col['c']=='')
        {
            if(is_string($col['f']))
                $this->aCols[$i]['c']=ucfirst($col['f']);
            else
                $this->aCols[$i]['c']=ucfirst(mysql_field_name($res,$col['f']));
        }
    }
    //Handle properties
    if(!isset($prop['width']))
        $prop['width']=0;
    if($prop['width']==0)
        $prop['width']=$this->w-$this->lMargin-$this->rMargin;
    if(!isset($prop['align']))
        $prop['align']='C';
    if(!isset($prop['padding']))
        $prop['padding']=$this->cMargin;
    $cMargin=$this->cMargin;
    $this->cMargin=$prop['padding'];
    if(!isset($prop['HeaderColor']))
        $prop['HeaderColor']=array();
    $this->HeaderColor=$prop['HeaderColor'];
    if(!isset($prop['color1']))
        $prop['color1']=array();
    if(!isset($prop['color2']))
        $prop['color2']=array();
    $this->RowColors=array($prop['color1'],$prop['color2']);
    //Compute column widths
    $this->CalcWidths($prop['width'],$prop['align']);
    //Print header
    $this->TableHeader();
    //Print rows
    $this->SetFont('Arial','',11);
    $this->ColorIndex=0;
    $this->ProcessingTable=true;
    while($row=mysql_fetch_array($res))
        $this->Row($row);
    $this->ProcessingTable=false;
    $this->cMargin=$cMargin;
    $this->aCols=array();
}
}

class PDF extends PDF_MySQL_Table
{

function Header()
{
    //Title
    $this->SetFont('Arial','',18);
    $this->Cell(0,6,'LISTADO DE USUARIOS',0,1,'C');
    $this->Ln(10);
    //Ensure table header is output
    parent::Header();
}
}
?>

EJEMPLO SENCILLO SIN TABLAS:
<?php
require('./fpdf/fpdf.php');
require('tablas_pdf.php');
$pdf=new FPDF();
$pdf->AddPage();
$pdf->SetFont('Arial','B',16);
$pdf->Cell(40,10,'¡Mi primera página pdf con FPDF!');
$pdf->Output();
?>

EJEMPLO CON TABLAS:
mysql_connect('localhost','root','');
mysql_select_db(bd_pruebas');
$pdf = new PDF();
$pdf->AddPage();
// Columnas Cabecera
$pdf->Table('select nombre_completo, username, email, nif from users');
$pdf->AddPage();
// Columnas cuerpo
$pdf->AddCol('nombre_completo',20,'','C');
$pdf->AddCol('username',20,'','C');
$pdf->AddCol('email',20,'','C');
$pdf->AddCol('nif',20,'','C');
$pdf->Output();