Ok thank you Manisha, now i've solved most of my problems, and my concern is about to customize and override the invoice. For that, i've following some recommandations found in the knowledge base and i've duplicate the default_pdfcontent.php in :
/ROOT_FOLDER/templates/MY_TEMPLATE/html/com_payplans/_plg/pdfinvoice/default_pdfcontent.php
that seems working fine. But now i wondering how to make downloaded invoice and invoice sent by email similar to on screen invoice? And if i want to override them, which file should i copy
Thanks