Hello,
in order to resolve font issues it is important to know what kind of transformations are being run for the previewer, e.g. what kind of documents the error affects. The most common transformation is of office documents to PDF via OpenOffice / LibreOffice. In that case you need to make sure that any fonts used in those office documents are installed into OpenOffice / LibreOffice. There are quite some good how-to guides out there for the different types of OS distributions.
Regards
Axel