If it's the model that was first sold in the U.S. starting in 2008, the manual is over to the left under "Helpful Links" (see 451 smart fortwo Owner's Manual). Don't know where you'd download a manual for a 2007 and earlier model.
I just realized the link on the left is an iPaper version of the manual, which you don't actually download but can view in your browser. For a PDF version (both Full and Quick manuals) that you asked for in your post, check Post #5 in this thread:
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