A better method would be to show the sizes in a Windows Explorer column, as discussed in this forum thread:
Displaying PDF Page Size in Windows Explorer.
But, if you really want to go with the file rename method, you may use the
rename tool, with the help of this script (also attached bellow).
function PageSize() {
var Size = '';
var Page = BatchFile.Pages(0);
if (Page) Size = Page.Width.toFixed() + 'x' + Page.Height.toFixed() + ' mm';
BatchFile.close();
return Size;
}
Select all the files you want to rename and start the rename tool. Click the tool rename formula field right arrow and, from the menu that will show up, open the scripts editor, menu item "Scripts>Manage Scripts...". From this script editor main menu, import the bellow attached script (after unzipped) and close the editor (saving the changes).
You can now type
[F]_[PageSize] in the tool rename formula field, to achieve the file name schema you are requesting.