I have opened a PDF with Inkscape and exported it in Plain SVG. However, when I open it in any browser, the text is rendered with a different font.
This happens because the font-family property in the SVG file might be set to a font that is not installed on the system. In my case, it was DejaVuSans.
You should open the SVG file in a text editor and replace all font-family:DejaVuSans with, for example, font-family:Arial.