Try The Free Dictionary:
An announcement represents merely teling everyone about something
A pronouncement is a formal statement of one's opinion.
At the end of the marriage ceremony, the official, under the power invested in him, "pronounces" rather than "announces" that the couple are now "man & wife".
announcement - definition of announcement by the Free Online Dictionary, Thesaurus and Encyclopedia.
1. a. The act of making known publicly.
b. Something announced.
c. A broadcast message, especially a program note or commercial.
2. An engraved or printed formal statement or notice, as of a wedding or a relocation.
pronouncement - definition of pronouncement by the Free Online Dictionary, Thesaurus and Encyclopedia.
1. A formal expression of opinion; a judgment.
2. An authoritative statement.
Hope this helps