Hi Dieter - the basic process that you'd use would be to extrude the circle downwards 5mm, then extrude the letters downwards 3mm and then select the circular solid, run Construct > Boolean > Difference and then select all the letter pieces as the cutting objects to cut them into the larger circular piece.

However, before you can do any of that you're going to need to clean up the curves because there are numerous places where your curves are "self intersecting" - where the curve has a sort of little loop in it where it crosses back over itself. This is what is likely causing you the most problems - when a curve crosses back over itself it no longer defines a proper inside and outside region and so it won't be possible to get a proper solid extrusion from it you'll get something that's weird and messed up in some way maybe without a top and bottom end caps or something like that.

Here's an example of one area of "self intersection":






Notice the little loop back over itself in the second curve in that corner area. To get a proper result you can't have any of these at all and you currently have one at every single sharp corner it looks like.


Another thing that could be problematic is the very short distance between the 2 outline curves, meaning this distance here:



Those curves are only about 0.08 units apart from one another, it can be difficult for the system to handle pieces that come so close to one another because at a certain point it decides they are close enough to need to be merged with each other. It's possible that they may be just far enough apart that it could maybe be ok but that's another possible problem area with your current curve layout, it tends to be better if surfaces and solids that you create don't have such a super thin areas in them like that.

If you try to extrude both an inner and outer outline like that at the same time, (if there were no self intersections), the extrusion would try to make only a super thin solid out of it, it would interpret the inside outline as supposed to be a hole.

- Michael