There isn't a global PDF page size because page size is related to the document pages, not the document itself. We can have a multi-pages PDF document with all different size pages. Probably not your case, but this happens very often.
When you check the document properties in a PDF reader (Acrobat, etc.) , what you see, related to the page size, is the size of current active page. You see also global document metadata, the one indexed by PDF Explorer, on that properties pages because developers opted, probably wrongly, to show that info together.
Because of this, impossibility do have a global page size constant, PDF Explorer don't gather that info. The possibility I see here is to have a specific tool to extract that info, and populate a user selected custom column(s) with it. Not the, impossible to define, page size, but the maximum, minimum, or average width and height values, of all the document pages. Then, and with the next PDF Explorer version, Dynamic Calculated Columns functionality, where we can enter mathematic expressions that can use other columns data to define its output, you will be able to easily calculate the area to invoice, and without the need to use Excel
Now that you mention the need, I'm going to see if I can evolve the current Search&Extract batch tool to accomplish also this get pages sizes task, and include it on next, almost ready, version.
