If you simply want to view a PDF file you can load it into a UIWebView.
let url : NSURL! = NSURL(string: "http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UIWebView_Class/UIWebView_Class.pdf")
webView.loadRequest(NSURLRequest(URL: url))
Swift 4.1 :
let url: URL! = URL(string: "http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UIWebView_Class/UIWebView_Class.pdf")
webView.loadRequest(URLRequest(url: url))
If you’d like to achieve more, a good framework is PSPDFKit.