Pages on my Macbook Pro has disappeared - why and can I get it back

The Pages tool on my MacBook Pro has disappeared - why and can I get it back - it seems Adobe has taken over my computer and won't let me open documents created in pages. And all documents being sent to me, which used to be in word format are coming in text format - can anyone advise me on what to do - how do I get rid of Adobe Acrobat Reader and get my Pages tool back