Why can I see a font even if it is not installed
If somebody sends you a Word document using a font that isn't installed on your computer, and they don't embed the font in the document, then Word will replace the font you don't have (Seravek in your case) with a default you do have (possibly Calibri, Arial or Times New Roman depending on your setup).
Confusingly, when you select the text and look at what font is being displayed, Word still says 'Seravek' (the name of the font you don't have).
Your options are:
Try and install the font yourself. Seravek requires a license.
Ask the person sending the document to embed the font in Word (as Thomas Weinbrenner suggests)
Ask the person to save the file as a static PDF which will embed the fonts automatically, but you won't be able to edit it in that format.
It is possible to embed fonts in documents.
So if this document uses a font which is not installed on your system, then this is probably a font embedded in this word document.