Handoff will be one of the coolest features of OS X Yosemite and iOS 8, letting you seamlessly transition between workflows on the two platforms, but unfortunately for owners of older Macs, it will require Bluetooth 4.0, which excludes Macs built before 2011, and even many built later. Peter Cohen of iMore explains how to check which version of Bluetooth your Mac has. If your Mac isn’t compatible with Handoff, a USB dongle that provides Bluetooth 4.0 may enable Handoff by Yosemite’s release. follow link
Go Back and Forth Fast in Preview
If you're reading a PDF in Apple's Preview software, and you follow a bookmark or an internal link to move around within the PDF, you can quickly return to where you were by pressing the keyboard shortcut Command-[ (that's Command-Left Bracket). Or, you can choose Go > Back.
The command works iteratively, so you can go back to just the previously viewed page or if you issue the command again, to the page before that, and so on. There's also an equivalent Go > Forward (Command-]).
OS X Yosemite’s Handoff Will Require Bluetooth 4.0