This is what I found on CIC's website:
"Completion check: Once you have submitted your application, we will check to determine that all required application forms have been properly completed and submitted, that the application processing fee has been paid, and that all required documents are submitted from the document checklist.
If your application lacks any of the requested documents, it will be returned to you. Failure to provide supporting documents in certain circumstances may result in the refusal of your application.
Acknowledgment of receipt: If your application is complete, it will be placed into processing. You will be sent a letter or e-mail that:
notifies you of this fact and provides you with your CIC office file number
sets out some basic instructions for contact with the CIC office processing your file
gives you a brief outline of future processing steps."
http://www.cic.gc.ca/english/information/applications/guides/EP7TOC.asp#ep76