He conseguido abrir el PDF con un wordPad y el resultado es este:
<body>
<div id="contenedor"><div id="menu_sup">
<table border="0" width="100%" height="100%">
<tr>
<td><img src="../../imagenes/logo.png" width="343px" height="95px" /></td>
<td><a href="../../inicio.php"><img src="../../imagenes/home.png" width="30px" height="30px" alt="Inicio" /></a></td>
<td>Bienvenido/a <a href="../../modulos/datos_personales.php">prueba</a></td>
<td> </td>
<td><a href="../../salir.php">Cerrar sesión</a></td>
</tr>
</table>
</div><div id="contenido_max">%PDF-1.7
%
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Por qu puede ser? Ayuda por favor!