Hi Frank,
Thanks for your interest in Syncfusion products.
Essential Diagram for WPF does not support importing *.edp files created from Symbol Designer into the Symbol Palette. However items can be added to the SymbolPalette in the following way:
//SymbolPaletteFilter creates a filter for the palette groups.
SymbolPaletteFilter sfilter = new SymbolPaletteFilter();
sfilter.Label = "Custom";
diagramControl.SymbolPalette.SymbolFilters.Add(sfilter);
//SymbolPaletteGroup creates a group and assigns a specific filter index.
SymbolPaletteGroup s = new SymbolPaletteGroup();
s.Label = "Custom";
SymbolPalette.SetFilterIndexes(s, new Int32Collection(new int[] { 0, 6 }));
diagramControl.SymbolPalette.SymbolGroups.Add(s);
//SymbolPaletteItem specifies the item which can be added to the group.
SymbolPaletteItem ss = new SymbolPaletteItem();
Path path = App.Current.Resources["CustomShape"] as Path;
ss.Content = path;
s.Items.Add(ss);
In this way any number of groups or items can be added to the SymbolPalette.
For more details pls refer the online documentation from the link mentioned below:
http://help.syncfusion.com/User%20Interface/WPF/DiagramNavigate to : Concepts and Features-->SymbolPalette
Please let us know if you have any concerns.
Regards,
Nikhil