How to save PDF file into MYSQL database? (PHP)

I’m trying to save all the information inserted by user into database, all the info are able to save except the pdf file.

My code:

usermanual.php

<div id="usermanualModal" class="modal fade">
    <div class="modal-dialog">
        <form method="post" enctype="multipart/form-data" id="usermanualForm">
            <div class="modal-content">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal">&times;</button>
                    <h4 class="modal-title"><i class="fa fa-plus"></i>&nbsp; Add New File</h4>
                </div>
                <div class="modal-body">
                    <div class="form-group">
                        <label for="um-area" class="control-label">Area</label>                         
                        <select id="um-area" name="um-area" class="form-control" placeholder="Area...">                 
                            <?php $usermanual->getUMAreas(); ?>
                        </select>                       
                    </div>
                    <div class="form-group">
                        <label for="um-subject" class="control-label">Subject</label>   
                        <input type="text" class="form-control" id="um-subject" name="um-subject" placeholder="Subject" required>
                    </div>
                    <div class="form-group">
                        <label for="um-description" class="control-label">Description</label>   
                        <input type="text" class="form-control" id="um-description" name="um-description" placeholder="Description" required>
                    </div>
                    <div class="form-group">
                        <label for="pdf" class="control-label"> File <span class="pdf-label">&emsp;(PDF file only)</span></label>
                        <input type="file" id="pdf" name="pdf" class="form-control" accept=".pdf" required/>
                    </div>
                </div>
                <div class="modal-footer">
                    <input type="hidden" name="usermanualId" id="usermanualId" />
                    <input type="hidden" name="action" id="action" value="" />
                    <input type="submit" name="save" id="save" class="btn save" value="Upload" />
                </div>
            </div>
        </form>
    </div>
</div>

usermanual_action.php:

if (!empty($_POST['action']) && $_POST['action'] == 'addFile') {
    $usermanual->area = $_POST["um-area"];
    $usermanual->subject = $_POST["um-subject"];
    $usermanual->description = $_POST["um-description"];
    $usermanual->filename = $_FILES["pdf"]["name"];
    $usermanual->insertUM();
}

usermanual.js:

$(document).ready(function() {  

    $('#addFile').click(function(){
    $('#usermanualModal').modal('show');
    $('#usermanualForm')[0].reset();
    $('.modal-title').html("<i class='fa fa-plus'></i> Add File");
    $('#action').val('addFile');
    $('#save').val('Save');
    });
    
    $(document).on('submit','#usermanualForm', function(event){
        event.preventDefault();
        $('#save').attr('disabled','disabled');
        var formData = $(this).serializeArray();
        $.ajax({
            url:"usermanual_action.php",
            method:"POST",
            data:formData,
            success:function(data){             
                $('#usermanualForm')[0].reset();
                $('#usermanualModal').modal('hide');                
                $('#save').attr('disabled', false);
                location.reload();
                usermanualData.ajax.reload();
            }
        })
    });

Usermanual.php:

    public function insertUM() {
        if($_POST['um-area']) {
            $this->usermanual = strip_tags($this->usermanual);              
            $queryInsert = "INSERT INTO ".$this->usermanualFiles." (area, subject, description, filename) VALUES('".$_POST['um-area']."', '".$_POST['um-subject']."', '".$_POST['um-description']."', '".$_FILES['pdf']['name']."')";

            mysqli_query($this->dbConnect, $queryInsert);

            $uploadDirectory = 'pdf/';

            $targetFile = $uploadDirectory . basename($_FILES['pdf']['name']);

            if (move_uploaded_file($_FILES['pdf']['tmp_name'], $targetFile)) {
                echo "The file " . basename($_FILES['pdf']['name']) . " has been uploaded.";
            } else {
                echo "Sorry, there was an error uploading your file.";
            }
            if ($_FILES['pdf']['error'] !== UPLOAD_ERR_OK) {
                echo "File upload failed with error code: " . $_FILES['pdf']['error'];
                exit;
            }
        }
    }

I have tried different ways, but the pdf file still not able to insert into database, following is the example outcome:

Please help if you have any solution, thanks a lot!