Reference? I doubt you have any of this Neardertal DNA, but there are many scientists who believe Neadertal DNA is widespread in modern day humans.
But an intact sample of pure Neandertal DNA? I think you are daydreaming or reading too much SF.
A Neandertal mitochondrial DNA sequence has been constructed and compared with homo sapien mitochondrial DNA. The comparison supported the idea that they didn't interbreed.
I wonder whether the Northern European troll myths are a folk memory of the last Neaderthals. Presumably places like Norway would have been their last holdouts.