PDF attachment error with wp_mail

I might recommend a slightly different approach.  Instead of sending the file, store the file on your server and send a link to the file.  Here's my thinking:

1. You can debug the PDF file creation and storage separately from the mail process
2. People who read email on handheld devices may not want to get printable attachments in the mail
3. You email traffic will be much "lighter" if you send a link instead of the entire document

Also, for security purposes, I would never use fopen() on an element of $_FILES.  There are way of testing for upload success, file integrity, etc.  These tests can help guard against attacks.  Maybe someone else can help with the "WordPress Way" of doing these things, but I can show you the PHP theory and practice of uploading a file in this code snippet.  The uploaded file is stored on the server and the browser presents a link to the client.

<?php // demo/upload_single_example.php
/**
 * Demonstrate how to upload a single file in PHP
 *
 * REQUIRED: Man Page References
 * http://php.net/manual/en/reserved.variables.files.php
 * http://php.net/manual/en/features.file-upload.php
 * http://php.net/manual/en/features.file-upload.common-pitfalls.php
 * http://php.net/manual/en/features.file-upload.errors.php
 *
 * http://php.net/manual/en/function.move-uploaded-file.php
 *
 * IMPORTANT: If dealing with large files
 * http://php.net/manual/en/ini.core.php#ini.upload-max-filesize
 * http://php.net/manual/en/ini.core.php#ini.post-max-size
 * http://php.net/manual/en/info.configuration.php#ini.max-input-time
 */
error_reporting(E_ALL);

// PHP 5.1+  SEE http://php.net/manual/en/function.date-default-timezone-set.php
date_default_timezone_set('America/Chicago');

// ESTABLISH THE BIGGEST FILE SIZE WE CAN ACCEPT - ABOUT 8 MB
$max_file_size = '8000000';

// ESTABLISH THE KINDS OF FILE EXTENSIONS WE WANT (USE UPPERCASE ONLY)
$file_exts = array
( 'XLS'
, 'XLSX'
, 'PDF'
, 'JPG'
)
;
$f_exts = implode(', ', $file_exts);

// ESTABLISH THE NAME OF THE DESTINATION FOLDER
$my_dir = getcwd();

// OR USE THIS TO PUT UPLOADS IN A SEPARATE FOLDER
$my_dir = 'storage';
if (!is_dir($my_dir))
{
    mkdir($my_dir);
}

// LIST OF THE ERRORS THAT MAY BE REPORTED IN $_FILES[]["error"] (THERE IS NO #5)
$errors = array
( UPLOAD_ERR_OK         => "Success!"
, UPLOAD_ERR_INI_SIZE   => "The uploaded file exceeds the upload_max_filesize directive in php.ini"
, UPLOAD_ERR_FORM_SIZE  => "The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form"
, UPLOAD_ERR_PARTIAL    => "The uploaded file was only partially uploaded"
, UPLOAD_ERR_NO_FILE    => "No file was uploaded"
, 5                     => "UNDEFINED ERROR"
, UPLOAD_ERR_NO_TMP_DIR => "Missing a temporary folder"
, UPLOAD_ERR_CANT_WRITE => "Cannot write file to disk"
, UPLOAD_ERR_EXTENSION  => "A PHP extension stopped the file upload"
)
;

// IF THERE IS INFORMATION POSTED
if (!empty($_POST))
{
    // IF THERE ARE ERRORS
    $error_code    = $_FILES["userfile"]["error"];
    if ($error_code)
    {
        trigger_error($errors[$error_code], E_USER_ERROR);
    }

    // GET THE FILE SIZE
    $fsize = number_format($_FILES["userfile"]["size"]);

    // SYNTHESIZE THE NEW FILE NAME FOR TEMPORARY STORAGE
    $fname = basename($_FILES['userfile']['name']);

    // FAIL IF THIS IS NOT AN ALLOWABLE EXTENSION
    $f_ext = explode('.', $fname);
    $f_ext = end($f_ext);
    $f_ext = strtoupper(trim($f_ext));
    if (!in_array($f_ext, $file_exts)) trigger_error("$f_ext NOT ALLOWED.  CHOOSE FROM $f_exts", E_USER_ERROR);

    // THE SERVER PATH TO THE FILE
    $my_path
    = getcwd()
    . DIRECTORY_SEPARATOR
    . $my_dir
    . DIRECTORY_SEPARATOR
    . $fname
    ;

    // THE URL PATH TO THE FILE
    $my_url
    = $my_dir
    . DIRECTORY_SEPARATOR
    . $fname
    ;

    // MESSAGES ABOUT THE UPLOAD STATUS, IF ANY
    $msg = NULL;

    // IF THE FILE IS NEW (DOES NOT EXIST)
    if (!file_exists($my_path))
    {
        // IF THE MOVE FUNCTION WORKED CORRECTLY
        if (move_uploaded_file($_FILES['userfile']['tmp_name'], $my_path))
        {
            $upload_success = 1;
        }
        // IF THE MOVE FUNCTION FAILED IT PROBABLY THREW A MESSAGE
        else
        {
            $upload_success = -1;
            trigger_error("MOVE TO $my_path FAILED", E_USER_ERROR);
        }
    }

    // IF THE FILE ALREADY EXISTS
    else
    {
        $msg .= "<br/><b><i>$my_url</i></b> already exists" . PHP_EOL;

        // SHOULD WE OVERWRITE THE FILE? IF NOT
        if (empty($_POST["overwrite"]))
        {
            $upload_success = 0;
        }

        // IF WE SHOULD OVERWRITE THE FILE, TRY TO MAKE A BACKUP
        else
        {
            $now    = date('Y-m-d-His');
            $my_bak = $my_path . '.' . $now . '.bak';
            if (!copy($my_path, $my_bak))
            {
                $msg .= "<br/><strong>Attempted Backup Failed!</strong>" . PHP_EOL;
            }
            if (move_uploaded_file($_FILES['userfile']['tmp_name'], $my_path))
            {
                $upload_success = 2;
            }
            else
            {
                $upload_success = -1;
                trigger_error("MOVE TO $my_path FAILED", E_USER_ERROR);
            }
        }
    }

    // PREPARE A REPORT OF THE SCRIPT'S SUCCESS OR FAILURE
    if ($upload_success == 2) { $msg .= "<br/>A backup was made and the file was overwritten" . PHP_EOL; }
    if ($upload_success == 1) { $msg .= "<br/><strong>$my_url</strong> has been saved" . PHP_EOL; }
    if ($upload_success == 0) { $msg .= "<br/><strong>It was NOT overwritten.</strong>" . PHP_EOL; }
    if ($upload_success < 0)  { $msg .= "<br/><strong>ERROR: $my_url NOT SAVED - SEE WARNING FROM move_uploaded_file()</strong>" . PHP_EOL; }

    // ADD FILE SIZE AND PERMISSION INFORMATION
    if ($upload_success > 0)
    {
        $msg .= "<br/>$fsize bytes uploaded" . PHP_EOL;
        if (!chmod ($my_path, 0755))
        {
            $msg .= "<br/>chmod(0755) FAILED: fileperms() = ";
            $msg .= substr(sprintf('%o', fileperms($my_path)), -4);
        }
    }

    // SHOW THE SUCCESS OR FAILURE
    echo $msg;

    // SHOW A LINK TO THE FILE
    echo '<br/>'
    . '<a href="'
    . $my_url
    . '" target="_blank">'
    . "See: $my_url"
    . '</a>'
    ;
}


// CREATE THE FORM FOR INPUT (USING HEREDOC SYNTAX)
$form = <<<EOF
<h2>Upload a File</h2>
<!--
    SOME IMPORTANT THINGS TO NOTE ABOUT THIS FORM...
    ENCTYPE= ATTRIBUTE IN THE HTML <FORM> TAG
    MAX_FILE_SIZE HIDDEN CONTROL MUST PRECEDE THE FILE INPUT CONTROLS
    INPUT NAME= IN TYPE=FILE DETERMINES THE NAME YOU FIND IN _FILES ARRAY
    ABSENCE OF ACTION= ATTRIBUTE IN <FORM> TAG CAUSES POST TO SAME URL
-->
<form enctype="multipart/form-data" method="post">
<input type="hidden" name="MAX_FILE_SIZE" value="$max_file_size" />
Find a file to Upload ($f_exts): <input name="userfile" type="file" />
<br/>Check this box
<input autocomplete="off" type="checkbox" name="overwrite" /> to <strong>overwrite</strong> existing files
</br><input type="submit" value="Upload" />
</form>
EOF;

echo $form;

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