The word "难以" is formed by combining the character "难", meaning "difficult", with the character "以", which functions as a grammatical particle indicating the means or manner of an action. Together, they create an adverbial compound that precedes verbs to express that something is hard to do, as seen in phrases like "难以理解" (hard to understand). This formation allows "难以" to modify verbs directly, conveying the sense of difficulty in performing the action.