var ad = AssemblyDefinition.ReadAssembly(@"C:pathtomylibrary.dll", new ReaderParameters { ReadSymbols = true });

Mono.Cecil.Cil.SymbolsNotFoundException was unhandled by user code
  HResult=-2147024894
  Message=No symbol found for file: C:pathtomylibrary.dll
  Source=Mono.Cecil
  StackTrace:
       at Mono.Cecil.Cil.DefaultSymbolReaderProvider.GetSymbolReader(ModuleDefinition module, String fileName)
       at Mono.Cecil.ModuleReader.ReadSymbols(ModuleDefinition module, ReaderParameters parameters)
       at Mono.Cecil.ModuleReader.CreateModule(Image image, ReaderParameters parameters)
       at Mono.Cecil.ModuleDefinition.ReadModule(String fileName, ReaderParameters parameters)
       at Mono.Cecil.AssemblyDefinition.ReadAssembly(String fileName, ReaderParameters parameters)