You can do this through CSS.
- In the Project Panel on the left side of the screen, go to Styles > Application and add in the call to use the font:
@font-face { font-family: 'Montserrat'; src: url('#{$resources}/Uploaded/Montserrat-Light.otf') format('otf'); font-weight: normal; font-style: normal;}
- Create a style definition that calls this font:
.custom-title {
font-size: 25px;
font-family:'Montserrat';
}
- Create your label and use the previously defined style:

If your font is available on-line, then you don't need to upload the font as a resource. Just change the source URL in the CSS definition to point to the on-line copy.
Hope this helps.
Allan