For any given font, the license is specified on the font's specimen page.
For example, near the bottom-right corner of https://fonts.google.com/specimen/Montserrat we can see that the license used is the SIL Open Font License. And from the SIL fonts FAQ[1]:
Please feel free to use SIL fonts in printed publications and PDF documents, including PDF documents posted on web pages. Such use is within the intended use of SIL fonts. No additional license or fee is required to use the fonts in a printed publication.
For example, near the bottom-right corner of https://fonts.google.com/specimen/Montserrat we can see that the license used is the SIL Open Font License. And from the SIL fonts FAQ[1]:
Please feel free to use SIL fonts in printed publications and PDF documents, including PDF documents posted on web pages. Such use is within the intended use of SIL fonts. No additional license or fee is required to use the fonts in a printed publication.
[1] http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=...