No, you can’t directly send money from a PayPal account to a Skrill account and vice versa. However, you can transfer funds between the two using an intermediary account, such as your bank account, or via a pre-paid Skrill or PayPal credit card.
To move funds either from PayPal to Skrill, or Skrill to PayPal, you would simply transfer the funds from your withdrawal account to your bank account or credit card, and then transfer the funds from there into the Skrill or PayPal account.