Trying to switch out the static attachment in an email to dynamic based on a Data Extension(DE).

The Static:

    %%[
    %%=AttachFile("FTP","AIDI.pdf")=%%
    ]%%

And what I'm tried to replace it with:

    %%[ var @Program,@ColumnProgramCode  set @ColumnProgramCode = Lookup("Program_Interest_G", "ProgramCode", "ProgramOfInterest", @Program)]%%
    %%[
    %%=AttachFile('FTP',%%@ColumnProgramCode%% +'.pdf')=%%
    ]%%

The DE is Program_Interest_G
the filed name is ProgramCode