The card does not speak of taking this with vitamin D or other omega-3 supplements. It describes the product as an additional source of omega-3 and of vitamins A and D and recommends consulting a doctor before use. The regimen according to the card: 3 capsules 3 times a day with meals, for 1 month.
General information (not a manufacturer's instruction): if you already take vitamin or omega-3 supplements, tell your doctor so that the total amount can be checked together.