It is perfectly possible to retrieve the PDF generated after you have done a check remittance (credit card, cash, etc.).
Simply go back to the Invoice module, then to Payment at the bottom left and All :
Then filter your Payment methods to find them more easily :
And finally, look in the Discount column (on the right) for discounts already applied :
As you can see in the discount there is a reference #DDigits (#Dchiffres), you can click on this reference :
This window appears :
Click on Generate remittance slip to preview the PDF.
The remittance slip :