Ok, I found the way, For future references, just implement the SubmenuName property in the plugin code:
public static string SubmenuName
{
get
{
return "oSoft";
}
}
Thank you for your prompt answer. Actually, I am the developer. What I need to know is how to place my plugins in a specific menu entry. I couldn't find anything in PaintDotNet.IPluginSupportInfo to specify the menu entry.