If you have a SimDif Pro Site you can add PayPal buttons to your site in the following way:
• Register a business account with PayPal.
• Set up buttons from inside your PayPal account.
• Open SimDif and go to Site Settings (top-right icon) select "E-Commerce Buttons" and enable them.
• Select Donate, Single, or Multiple button types, and click Apply
• Go to "Add a New Block" from one of your pages and select 'E-commerce'.
• Click on the e-commerce button block and paste the code for the button you want to set up.
Watch the tutorial video:
How To Add PayPal Buttons