When connecting an HDD to a different computer, are non-system partitions accessible?

My hard drive consists of two partitions:

• C:, the system partition containing Windows 8.1 and my programs,
• D:, a regular partition where I put all my documents and files.

I plan to buy an additional SSD and put the system partition on it (clean install of Windows 10 TP). I would like to keep using the D: partition of my old drive. Does this work out of the box? Say, I remove the old HDD and connect the new SSD, then install Windows 10, and finally connect the old HDD to have access to data from D:. Will this work?

It will work, but you will want to remove the partition with windows on the hdd. It may or may not try to boot to that partition if you don’t remove it, depending on your exact setup. If you don’t want to remove it then you should dual boot the system for both os’s and set the primary boot partition to your ssd.