When I used the term hidden I wasn’t using it in the traditional CAD sense. I’m using the term to describe how one object can’t be seen because it is behind another object.
Lets do a little project here to demonstrate what I mean. Starting with a new sheet, draw a rectangle using single line mode. Set the fill color to green and solid pattern. Select the fill tool and click inside the rectangle. Notice that the top line of the Inspector says 1 polygon. Fills are associated with polygons, to change the color or fill pattern the polygon must be selected. If you switch to object properties -> data tab in the Inspector you will now see the show frame and show fill options.
Draw a small circle inside the rectangle on the left side, as soon as it’s done the circle disappears, the circle is behind the fill color. The Inspector shows 1 circle is selected so go to the Edit menu and open the Arrange submenu and click on “Bring To Front”. Your circle now appears. Click on an empty part of the drawing to deselect the circle, in the Inspector click the Fill Properties icon and change the color to blue. Go back to the Fill tool and click inside the circle. Nothing seems to happen but the top of the inspector says 1 polygon. Go to the Arrange submenu and “Bring To Front”.
On the right side of the rectangle create an oval, again “Bring To Front”. Deselect everything and change color to magenta. Fill the oval and again “Bring To Front”, I don’t know why we keep needing to use bring to front, you would think the object being worked with would be on top by default.
Make a third circle and have it intrude into the oval and extend outside the rectangle. Deselect all and change the fill color to brown, now use the fill tool and click inside this circle and in the green area of the rectangle, Bring To Front and see that the oval and the bottom line of the rectangle have formed a boundary limiting the color between the oval and the rectangle bottom. To fill in the circle go to Edit and undo the fill, now select the circle then the Fill tool (circle deselects), hold the shift key and select the circle again, then “Bring To Front”. The circle should be filled.
I have also noticed that making each object one at a time eliminates those extra lines.
I hope this allows you to complete your project.