is it possible to select some polylines for example n. 5 rectangles and know immediately the sum of its perimeters? to avoid selecting a polyline at a time?
Yes, loading the arx application "geomprops" from the Russian site http://www.maestrogroup.com.ua/support/geomprops.zip.
once loaded the one suitable for the version of your autocad (from 2006 to 15), activating the "prorpita" panel of autocad you will find added the section "geometrical properties" with the voices area, volume and lunghrezza (totali)