Looks clean, I like the soft purple colour scheme 
- I would prefer the page numbering to be "1 / 42" etc instead of just "1"
- on page 5, the text in the purple box is not centered correctly (no top-bottom-centering if you understand)
- page 6: "empfohlene Luftkühlung Konfiguration" should be "empfohlene Luftkühlungs-Konfiguration"
- you could also add small titles for each step of the mounting procedure, e.g. "installing Motherboard IO shield" or "2.5 inch SSD installation (optional step)" (this is actually done with the "AiO installation" parts of the manual)
- page 33 does not clearly state the up- and downsides of removing this part. Personally, I don't get it. Is this the FE GPU air duct? Under which circumstances should I remove this said part or not?
- page 37: in english it's "case feet", not "case feets" and german would be "Gehäusefüße"
- page 37: "PCIe Slotblende" -> "PCIe-Slotblenden"
- page 37: "Grafikkarten Slotabdeckung" -> "Grafikkarten-Slotabdeckung"
- page 38: "www.dan-cases-com" -> "www.dan-cases.com"
