Hello Jenny,
Neither Arial Black nor Helvetica are installed on our servers and so unavailable for PDF. If you require Arial Black or Helvetica in the generated PDF, you can upload the font files via the standard CSS rule. Example:
@font-face
{
font-family: 'Helvetica';
src: url('https://example.com/fonts/HelveticaBold.ttf') format(truetype);
font-weight: normal;
font-style: normal;
}