: The ".11" suggests this is only one part of a larger file, meaning even a "clean" download would likely be unusable without the other 10 parts.
: Ensure your operating system shows full extensions. Windows and macOS often hide extensions by default, which means a file named document.pdf.exe might just look like document.pdf to an unsuspecting user. A-Rider-Needs-No-Pants.avi.11.pdf
The presence of the in the filename is the most poignant part of the riddle. It signifies incompleteness. : The "