visual studio - Referenced DLL in VisualStudio can't find its own DLL C# -

i'm using external dll handle pdf exports in c# project. i've added external dll reference in visual studio, added appropriate using statements, intellisense shows sorts of methods , properties when type out namespace, , same reflected in object explorer.

however, when run application, program throws run-time exception because external dll can't find dll lives in same directory external dll.

to make matters more confusing, program doesn't complain if copy every single dll directory of 1 want reference debug folder of program, shouldn't have this.

thanks in advance.

what need check "copy output directory", "always copy" in properties of dll in vs. otherwise dll not automatically copied in output, , program can not run.

i think other question might you: msbuild doesn't copy references (dll files) if using project dependencies in solution