Could you post an image of your problem?

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[Link to www.3dprevis.com]

when you extrude shapes (splines) they need to be closed splines to extrude as a solid object. You need to use the editable spline tools to close the spline shape then add an extrude modifier. Convert to editable spline (if its not already)> pick the two end points> hit fuse to bring the points to the same location>then hit weld to join them together.

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on viewport you can see 2 objects. right one is 2 objexts extruded and boolean to make this form and left is one more tried to extrude. But it is just a square from autocad. and it is closed spline. it is just driving me crazy. some objects from cad extrude as solid objects and some extrude just their outlines.

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sorry guys.
i found out what was the problem, the lines were open but were made in one software that puts them so close and doesnt weld them. thank you for your replies.
bye

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