Export to pdf when viewed produces thick lines in the text.

I recently watched a webinar on " Typography & Fonts Master Class for CorelDraw . At around the 1 hour mark someone asks if when you export to pdf and then view that pdf it looks like some of the text has thicker lines than it's supposed to be. The lady answering that question says to go into settings and uncheck the "increase the width of thin lines" which is there by default.

Please can you tell me where to find it?

This does not happen when the file is printed but it is annoying when sometimes my customers ask whats wrong with the text.