index.php

<td>
    <input type="file"  id="fileIMG3" name="fileIMG3" 

 accept="application/pdf" >
</td

  

   
sender.php
  
if(!empty($_FILES['fileIMG3']['type'])){
    $target_path3 = $_FILES['fileIMG3']['name'];
    $valid_extensions3 = array('pdf');
    $temporary3 = explode(".", $_FILES["fileIMG3"]["name"]);
    $file_extension3 = end($temporary3);


    if((($_FILES["fileIMG3"]["type"] == "img/pdf")) 
        && in_array($file_extension3, $valid_extensions3)){
        $target_path3 = "img/";
        $target_path3 = $target_path3.basename
($_FILES['fileIMG3']['name']);
       move_uploaded_file($_FILES['fileIMG3']['name']
,$target_path3 );
        $uploadedFile3 =   $target_path3;

    }

}
  

   
sendData.js
  
$(document).ready(function(){
    $("#sendForm").on('submit', function(e){
        e.preventDefault();
        $.ajax({
            type: 'POST',
            url: 'sender.php',
            data: new FormData(this),
            contentType: false,
            cache: false,
            processData:false,
            beforeSend: function(){
                $('.submitBtn').attr("disabled","disabled");
                $("#sendForm")[0].reset();
            },
            success: function(msg){

                $('#fupForm').css("opacity","");
                $(".submitBtn").removeAttr("disabled");
            }
        });
    });

    //file type validation
    $("#send_data").change(function() {
        var file = this.files[0];
        var imagefile = file.type;
        var match= 
["image/jpeg","image/png","image/jpg", "img/pdf"];
        if(!((imagefile==match[0]) || (imagefile==match[1]) 
|| (imagefile==match[2]) || (imagefile==match[3]))){
            alert('Please select a valid image file 
(JPEG/JPG/PNG/PDF).');
            $("#send_data").val('');
            return false;
        }
    });
});