The Media Library’s size limit for individual files is 20 MB (20480 kBytes). If the file you’re trying to upload is larger than that, the Media Library will not allow you to upload it. You then have a couple of options to reduce the file's size:
- Acrobat for PDFs: you can chose save file using the smallest file size
- PhotoShop for images: you can re-size the image to a smaller resolution (72 dpi for the web)
If your PDF is still too large, consider breaking up the original file (for example, the Word file) into parts, create two or more separate PDFs, then upload each one.