If you need to email your thesis with limited size, compressing your PDF files is the easiest way to solve this problem.
1. Click Compress on Editor ；
2. Or click main menu Tools -> Editor -> Compress;
3. Select the quality of the compressed file. If clicking Batch, you can add more files to compress simultaneously;
4. Save it as a new PDF or Share via Email, Airdrop, iCloud and etc.