Kim K Suing Old Navy -- You Can't COPY Me! [DOCS]

There is only ONE Kim Kardashian -- and now she's declaring a legal war on Old Navy for using a Kim K look-alike in a recent ad campaign ... TMZ has learned. Kim is filing a lawsuit against the clothing giant  -- claiming they intentionally used a look-alike in an effort to dupe the public into thinking Kim was affiliated with Old Navy. We're told Kim is especially furious that Old Navy has been tweeting to her page about the look-alike -- in an effort to gain even more publicity. One of those tweets read, "@CBSNEWS reports that Old Navy's Super CUTE star looks like @kimkardashian. #LOL. What do you think?"We're told Kim believes the copycat campaign has damaged her wallet somewhere in the range of $15 to $20 million.