In Minecraft (PC), normally, you can't duplicate blocks/items in Survival Mode using the anvil. However, they are duplicable in Creative Mode. Just follow the steps you would normally follow in the CE (Console Edition) to dupe blocks with the anvil, but in Creative Mode and in the PC Edition. When you go to the Survival Inventory in Creative Mode, try to move the blocks from the inventory. You will see they do not disappear, while in Survival/Adventure Mode they do.

Steps to reproduce:
1. Take 2 blocks, one in each inventory slot
2. Open the anvil
3. Shift-click the block from the left
4. Repeat step 3 but this time with the block from the right
5. Shift-click the anvil slot where the blocks are
6. You'll see there are 4 blocks now. Close the anvil GUI and open the Creative GUI
7. Open the Survival Inventory
8. Click each of the stacks. You'll see none of them disappear and you are free to move them.