Architect plan editing

Cropping would be my preferred way of reducing a large page to just a smaller portion of that page. You can access the crop tool by e.g. right-clicking on the page in the page thumbnails navigation pane on the left, and then select "Crop Pages...", or by selecting the crop function from the "Organize Pages" toolset in Acrobat DC.

The only potential downside of cropping is that the original page content is still available, which means that first of all, the document size will not change, but also, that somebody with access to the crop tool can restore the original content.