Views: add (link to file field) to image field
First add the "Content:File" field
Check "Exclude from display" (hidden)
Under "Formatter" select "URL to file"
Then add your Image field and uncheck "Link this field to the original piece of content" or something similar
Click on "Rewrite Results" and check "Output this field as a link"
In the "Link path" textbox add "Replacement Pattern" from the file field ([field_file] == Content: File, for example)