If you think you will be converting PDF documents that will contain foreign languages, such as Hebrew, Arabic, Thai and others, you may need to download the Adobe Reader Font Pack for your version of Adobe Reader.

The font pack for the Adobe Reader DC can be found here: 32-bit Font Pack and Spelling Dictionary for Acrobat Reader DC

You can also follow the instructions shown in Adobe Reader when opening the PDF file. The reader application will direct you where to download and install it's latest supported font packs.