This is one of the common problems faced by PDF users. PDF files get corrupted while transferring from one side to other. Weak or interrupted network connection is the main cause. Either you have a bad network connection or your client has. As we know network connection must be in good state for both uploading and downloading files. But it's not a big mess, still you may try these:
- Instead of sending the files via email just upload them to any server such as Adobe Sendnow or DropBox. And, send the link to your client and ask her to download the files from there.
- If this may not possible then put all your files into a RAR or ZIP file and then send it to your client. Compressed file is easily shared over the network and it's a good way to transfer data and other files from one place to other.
Hope this information will be helpful.