The maximum file size is 20MB.  The estimated number of pages in a 20 MB scanned PDF document is:

• Plain text, correspondence, pleadings, etc. 120 - 500 pages
• Tables, charts, extensive graphics 16 - 80 pages
• Condensed transcripts 40 - 60 pages

If you need to send more pages, you can split your PDF document into multiple parts and then send them back to back.