Our project has built using the Bootstrap Framework. Customization of global styles, such as font-family and other settings of the typography, also a project as a whole, is carried out by changing the values of the variables responsible for a property according to official Bootstrap documentation. All variables and their values that have been customized are placed in a separate file ..\Bootstrap\scss\_custom.scss. In particular, the variable $font-family-sans-serif is responsible for the font-family.
You should change its value and recompile sass-styles.
If you do not use scss and preprocessors, find the files
..\Bootstrap\dist\css\bootstrap.scss and ..\Bootstrap\dist\css\bootstrap-reboot.css
There you can change the value of the font-family for a body to the font whatever you want to use.