Let's just use "Seitenvorschau" (the noun), instead of "Seite vorschauen". I'm confident we can't say the latter anyway.
Please make sure you change this everywhere it's being used, not only in Pages app.
In the future, we actually can use a similar term for other content elements as well such as
- "Vorschau des Kontakts" (description)
- "Assetvorschau" (combination of terms)
- or even just "Vorschau" (will be clear in most contexts)