Set MIME type to applicaiton/octet-stream
to trigger a download, rather than displaying the PDF in the browser plugin. (This would make web-optimized / linerized PDFs moot; but it might be a good practice to use this feature.)
Information density of PDF files should not exceed one Mega(1024^2)-byte per page (the inverse should not be lower than 1 page per MB), with an ideal density of less than 0.5 MB/page or more than the inverse 2 pages per MB.
Display page count as well as file size, as the file size might not convey as much meaning to users as "114 pages".