how do i copy and paste across 2 hammer maps?

It IS possible to copy items between different maps if they're open in separate 'tabs' (just load a map then load another without closing), not Hammer instances.

I just select what I want on one map, ctrl-C, go to another map I want it in, ctrl-V, and its done

Obsidian2007 said:

can you send a screen shot?

Click to expand...

With a map already open in Hammer, go "File -> Open..." and open a map from there as you would normally. Now you have more than one map open at once within one instance of Hammer.

There are a couple of ways to switch between them; the simplest is to click on "Window" at the top of your screen, and then select whichever map file you want to switch to underneath the part that says "Messages"

You can also cycle through the files listed here by pressing "Ctrl+Tab", or "Ctrl+Shift+Tab", but keep in mind that this will also cycle through the "Messages" window, so you may want to disable that by clicking on the "Messages" line with the check next to it, or pressing "Alt+F3" to toggle. This is my preferred way of switching between different map files, as it's quick
You can also try messing with these window buttons at the upper right, which can also allow you to display multiple maps at the same time, but IMO it's a bit harder to use (if you minimize a window and can't find it, you can maximize it again using the first method I listed)

This is also the main way I use to close a map file once I no longer need it (you'll want to close any large files when you're done with them, as Hammer is badly optimized so they may cause it to lag), though you can also close the current file by going "File -> Close"
Hope this helped!