function checkFileExtensionArfchivos(elem) {
        var filePath = elem.value;

        if (filePath.indexOf('.') == -1)
            return false;

        var validExtensions = new Array();
        var ext = filePath.substring(filePath.lastIndexOf('.') + 1).toLowerCase();

        validExtensions[0] = 'txt';
        validExtensions[1] = 'doc';
        validExtensions[2] = 'xls';
        validExtensions[3] = 'pdf';
        validExtensions[1] = 'docx';
        validExtensions[2] = 'xlsx'

        for (var i = 0; i < validExtensions.length; i++) {
            if (ext == validExtensions[i])
                return true;
        }

        var who2 = elem.cloneNode(false);
        who2.onchange = elem.onchange;
        elem.parentNode.replaceChild(who2, elem);
        alert('Extension ' + ext.toUpperCase() + ' no valida!');
        return false;
    }

 function checkFileExtension(elem) {                                              
        var filePath = elem.value;                                                
                                                                                  
        if (filePath.indexOf('.') == -1)                                          
            return false;                                                         
                                                                                  
        var validExtensions = new Array();                                        
        var ext = filePath.substring(filePath.lastIndexOf('.') + 1).toLowerCase();
                                                                                  
        validExtensions[0] = 'jpg';                                               
        validExtensions[1] = 'jpeg';                                              
        validExtensions[2] = 'bmp';                                               
        validExtensions[3] = 'png';                                               
        validExtensions[4] = 'gif';                                               
        validExtensions[5] = 'tif';                                               
        validExtensions[6] = 'tiff';                                              
        /* validExtensions[7] = 'txt';                                            
        validExtensions[8] = 'doc';                                               
        validExtensions[9] = 'xls';                                               
        validExtensions[10] = 'pdf';*/                                            
                                                                                  
        for (var i = 0; i < validExtensions.length; i++) {                        
            if (ext == validExtensions[i])                                        
                return true;                                                      
        }                                                                         
                                                                                  
        var who2 = elem.cloneNode(false);                                         
        who2.onchange = elem.onchange;                                            
        elem.parentNode.replaceChild(who2, elem);                                 
        alert('Extension ' + ext.toUpperCase() + ' no valida!');                  
        return false;                                                             
    }