If you want to open additional area from solder mask (more than pads area), you can do it in following way:
Select Top Mask or Bottom mask (depending on where heatsink is) from drop-down box on drawing panel. Then choose shape type (filled rectangle, ellipse or polygon) and define its points on ...

Currently, DipTrace video tour is without sound.

I see the problem. Thank you. It will be fixed in next version.

If you design board without schematic, right click in PCB Layout on any pattern you want to change and select "replace pattern" in submenu. Then choose new pattern and change "Apply to" option to "Similar type patterns".

If you design project with schematic, you should replace patterns for all ...

For manual routing, just route wires on single layer.
For shape auto-router, open auto-router setup, go to settings tab, click on "Use priority layer direction" option. Then turn-off Top or Bottom layer.
For grid auto-router, open auto-router setup, unselect option "use all layers" and set number of ...

3D view feature is currently in progress. It will be added in next version.

So, if I want to keep analog and digital power as separate nets, then I should not connect them to the actual power in the schematic. I should connect them only when routing the PCB. Is that right?

If you want to keep analog and digital grounds as separate nets, you can connect them via 0 Ohm ...

Welcome to the forum!
I hope this will be right place for communication between DipTrace users and other people involved in electronic industry.