What i get is that you want welcome.php code in HTML page??
Make your form like this
<form action="<?php $_Server['PHP_SELF]??>" method="post">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
and on the top of the page(before ) you can write php scripts(ie code of welcome.php)
Hope it'll help you