Update file field from PHP in MySQL

I have a table that stores the names of those responsible for some minutes, so once the minutes are signed I upload them so that they are included in the column of the person in charge. But when trying to upload the record, this appears:

This is the UPDATE that I have:

<?php
if(isset($_FILES["acta"]))                               
           $acta = ($_FILES['acta']);
        else
            $acta =NULL;
    $orden=intval($_POST['mod_orden']);

    $sql="UPDATE asignacion_pc SET Nombre='".$nombre."', Cargo='".$cargo."', Equipo='".$equipo."', Cedula='".$cedula."', Celular='".$celular."', condicion='".$condicion."', estado='".$estado."', acta='".$acta."' WHERE orden='".$orden."';";

And the database:

Updated

<?php
    if (isset($con))
    {
?>

<div class="modal fade" id="myModal20" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        <h4 class="modal-title" id="myModalLabel"><i class='glyphicon glyphicon-edit'></i> Entrega de equipo corporativo</h4>
      </div>
      <div class="modal-body">
        <form class="form-horizontal" method="post" id="editar_asignacion_pc" name="editar_asignacion_pc" enctype="multipart/form-data" action="asignacion_pc">

        <div id="resultados_ajax2"></div>
          <div class="form-group">
            <label for="Nombre2" class="col-sm-3 control-label">Nombre</label>
            <div class="col-sm-8">
              <input type="text" class="form-control" id="Nombre2" name="Nombre2" placeholder="Nombre" required>
                <input type="hidden" id="mod_orden" name="mod_orden">
            </div>
          </div>
          <div class="form-group">
            <label for="Cargo2" class="col-sm-3 control-label">Cargo</label>
            <div class="col-sm-8">
              <input type="text" class="form-control" id="Cargo2" name="Cargo2" placeholder="Cargo" required>
            </div>
          </div>
          <div class="form-group">
            <label for="Equipo2" class="col-sm-3 control-label">Equipo</label>
            <div class="col-sm-8">
              <select class="form-control" name="Equipo2" id='Equipo2' required>
              <option value="">Seleccione un equipo</option>  
              <option value="Lenovo Thinkpad E460">Lenovo Thinkpad E460</option>
              <option value="Lenovo Thinkcenter">Lenovo Thinkcenter</option>       
              <option value="HP prodesk 600 g1 sff">HP prodesk 600 g1 sff</option> 
              <option value="HP probook 430 G3">HP probook 430 G3</option>
              <option value="HP Pavilion x360">HP Pavilion x360</option> 
              <option value="HP probook 450g">HP probook 450g</option>         
              </select>
               </div>
          </div>
      <div class="form-group">
            <label for="Cedula2" class="col-sm-3 control- 
        label">Cedula</label>
            <div class="col-sm-8">
              <input type="text" class="form-control" id="Cedula2" 
         name="Cedula2" placeholder="Cedula" required>
            </div>
          </div>
                  <div class="form-group">
            <label for="Celular2" class="col-sm-3 control- 
               label">Celular</label>
            <div class="col-sm-8">
              <input type="text" class="form-control" id="Celular2" 
                name="Celular2" placeholder="Celular" required>
            </div>
          </div>    
             <div class="form-group">
            <label for="condicion2" class="col-sm-3 control- 
                label">Condicion</label>
            <div class="col-sm-8">
               <select class='form-control' name='condicion2' 
               id='condicion2' required>
                    <option value="">Seleccione un Tipo de 
                 condicion</option>
                    <option value="Nuevo">Nuevo</option>
                    <option value="Usado">Usado</option>
                </select>
            </div>
          </div>    
             <div class="form-group">
            <label for="estado2" class="col-sm-3 control- 
                 label">Estado</label>
            <div class="col-sm-8">
               <select class='form-control' name='estado2' id='estado2' 
                 required>
                    <option value="">Seleccione un Tipo de estado</option>
                    <option value="Activo">Activo</option>
                    <option value="Inactivo">Inactivo</option>
                </select>
            </div>
          </div>    
             <div class="form-group">
            <label for="acta" class="col-sm-3 control-label">Acta</label>
            <div class="col-sm-8">
              <input id="acta" type="file" name="acta" > 
            </div>
          </div>

      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Cerrar</button>
        <button type="submit" class="btn btn-primary" id="actualizar_datos">Guardar datos</button>
      </div>
      </form>
    </div>
  </div>
</div>
<?php
    }
?>