如何将PDF签名写入MySQL数据库

我已经开发了一份PDF表格，供公司跟踪里程费用。用户完成操作后，用户可通过单击按钮提交文档。提交后，它将发布到php网页，并将字段信息写入MySQL数据库。一切都很好，但是我们要求用户使用PDF电子签名字段对文档进行签名。我无法将签名发布或写入数据库。字段名称是签名。任何帮助都会很棒。

代码如下（无签名）：

<?php

    include_once('../php/functions.php');

    $sig_month = $_POST['sig_month'];
    $sig_day = $_POST['sig_day'];
    $sig_year = $_POST['sig_year'];
    $mileage_rate = $_POST['mileage_rate'];
    $form_id = $_POST['form_id'];
    $submission_date = $_POST['submission_date'];
    $signed = $_POST['signed'];
    $employee_name = $_POST['employee_name']; 

    if(strlen($sig_month) == 1){
        $sig_month = "0".$sig_month;
    }
    if(strlen($sig_day) == 1){
        $sig_day = "0".$sig_day;
    }

    $employee_initial = $employee_name[0];
    $employee_explode = explode(" ", $employee_name);
    $employee_email = $employee_initial . $employee_explode[1];
    $employee_email = strtolower($employee_email) . "@fbhi.net";

    $mileage_rate = "0.".$mileage_rate;

    $query="SELECT * FROM employee WHERE email = '$employee_email'";
    $ifExists = ifExists($query,$db_con);   

    if($ifExists > 0){

        $result = queryMysqli($query,$db_con);

        while($row = mysqli_fetch_array($result)){

            $employee_name = $row['first_name'] . " " . $row['last_name'];
            $error = 0;
            $success = 0;
            $x = 1;

            $query1 = "DELETE FROM mileage_form WHERE form_id = '$form_id'";
            if(!queryMysqli($query1,$db_con)){

                $error++;

            }           

            while($x < 8){

                $month = $_POST['month_day'.$x];
                $day = $_POST['day_day'.$x];
                $year = $_POST['year_day'.$x];
                $purpose = $_POST['purpose_day'.$x];
                $miles = $_POST['miles_day'.$x];

                if(strlen($month) == 1){
                    $month = "0".$month;
                }
                if(strlen($day) == 1){
                    $day = "0".$day;
                }

                if($employee_name != "" && $mileage_rate != "" && $month != "" && $day != "" && $year != "" && $purpose != "" && $miles != "" && $form_id != "" && $submission_date != "" && $sig_month != "" && $sig_day != "" && $sig_year != "" && $signed == "t"){

                    $query = "INSERT INTO mileage_form (employee_name,mileage_rate,month,day,year,purpose,miles,sig_month,sig_day,sig_year,submission_date,signed,form_id)
                    VALUES ('$employee_name','$mileage_rate','$month','$day','$year','$purpose','$miles','$sig_month','$sig_day','$sig_year','$submission_date','$signed','$form_id')";
                    if(!queryMysqli($query,$db_con)){
                            $error++;
                        }else{
                            $success++;
                        }

                }
                $x++;
            }

            if($error != 0){
                echo "Something went wrong! Your mileage claims did not submit!";
            }

            if($success != 0){
                echo "<center>Mileage claims have been submitted for <br /><font size=6><strong>$employee_email</strong/></font><br />If this is not the correct email, contact your IT Administrator immediately!";
            }else{

                echo "Your mileage form is incomplete. Ensure all of the required information is finished, and then resubmit your form.";

            }


        }

    }else{

        echo "<center>Sorry, your email is not registered in our database. If you are positive your email is $employee_email, please contact your IT Administrator";

    }
?>