Hi,
Related with your Gmail and Google Drive, and DropBox.
If you using Web Browser to upload these files, you will need a "Network Prevent for Web" with an Proxy and ICAP to block it.
If you using any apps (Like Dropbox for example) you can block it creating a rule in your Endpoint Prevent.
Please have a look the following post and try do it like a test. (The rule will block all PDF file transfer from any source to any destination)
https://www-secure.symantec.com/connect/articles/dlp-policy-block-uploading-file-type-web-httphttps
I hope it helps.
Lucas M. Pinheiro