Right; this has nothing to do with ArchiCAD and everything to do with trying to use Excel with Pages. Pages does not understand Excel clipboard format.
You have to understand that Pages was designed to work with Numbers not Excel. Numbers understands Excel however. So if you export from ArchiCAD to Excel and then open the Excel file in Numbers (thereby converting it to an Apple format) then you can paste from Numbers into Pages.
Testing just now, I found that even using numbers doesn't give A perfect solution. Everything pastes into Pages but all the graphics paste as individual elements in a grid layout and the remaining spreadsheet content pastes as a single table. Better than trying to paste from Excel though.
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