There are two ways to solve this problem.
Option 1: Use %20 to represent a space
link:assets/Marketplace%20-%20Guide.pdf[Manual^]
Option 2: Use {space} or {sp} to represent a space
link:assets/Marketplace{space}-{space}Guide.pdf[Manual^]
Technically, option 1 is more correct since you're not supposed to have spaces in a URL. %20 is a URL-encoded space, hence a legal way to put a space in a URL.
-Dan