The two fields category and language narrows the function Search down.

Search for	Input line "search"	Choose category
Declaration of Conformity		Approvals / Zulassungen
Flyers		Product information / Produktinformation
Presentations		Documents / Dokumente
Press releases		Documents / Dokumente
Product(name)	e.g. DE900 -> click Button Search
User Manuals		Manuals / Anleitungen

In addition the Advanced Search helps to find documents within a predefined key (level 1..3)