<form action="upload_file.php" method="post" enctype="multipart/form-data" target="my_iframe">
    Select a file: <input type="file" name="upload">
    <input type="submit">
</form>

$allowedExts = array("doc", "docx");
    $extension = end(explode(".", $_FILES["file"]["upload"]));

    if (($_FILES["file"]["size"] < 200000)
    && in_array($extension, $allowedExts)) {
        if ($_FILES["file"]["error"] > 0)
        {
            echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
        }
        else
        {
            echo "Upload: " . $_FILES["file"]["upload"] . "<br />";
            echo "Type: " . $_FILES["file"]["type"] . "<br />";
            echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />";
            echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br />";

            if (file_exists("Proposals/" . $_FILES["file"]["upload"]))
            {
                echo $_FILES["file"]["upload"] . " already exists. ";
            }
            else
            {
                move_uploaded_file($_FILES["file"]["tmp_name"],
                "Proposals/" . $_FILES["file"]["upload"]);
                echo "Stored in: " . "Proposals/" . $_FILES["file"]["upload"];
            }
        }
    } else {
        echo "Invalid file";
    }

$extension = pathinfo( $_FILES["file"]["upload"], PATHINFO_EXTENSION);

die($extension);

<iframe name="my_iframe" src="upload_file.php"></iframe>

$_FILES["file"]["upload"]

$_FILES["upload"]["name"]

$_FILES["file"]["size"] **To** $_FILES["upload"]["size"]

$_FILES["file"]["type"] **To** $_FILES["upload"]["type"]

$_FILES["file"]["tmp_name"] **To** $_FILES["upload"]["tmp_name"]

if (($_FILES["file"]["size"] < 200000) && in_array($extension, $allowedExts)) {

<input type="file" name="upload">

$_FILES["file"]["size"]

$_FILES["upload"]["size"]

<input type="file" name="upload">
                  HERE ----^