A: .pfb is a PostScript font format (old). You want .ttf or .otf for modern systems. Find a different download source.
HK Modular Bold is a strong modular display font ideal for bold headings and branding; before downloading a "full" version labeled free, verify the license and source to ensure legal, safe use. If you want, I can search for official sources or alternatives — say “find sources” and I’ll look them up.
It’s an excellent choice for H1 tags. Its thick strokes ensure that your message is the first thing a visitor sees.