Thanks.  My desire is to use the old win 7 drive so that all the data from the old computer would be available on the new computer without having to copy all of it. If it is used as a secondaty data drive would the applications that remain on it work on the new pc if it is not a bootable drive?   Also, is it advisable to assign another drive letter other than C to the HDD?   note: the win 7 OS is 32 bit.

Windows 10 will automatically assign a drive letter to secondary data drive.  I do not think applications installed via 32 bit Win 7 will run on Win 10 for two reasons. The applications are not detected by Win 10 which stores its native programs in the ssd under Program Files folder.  On the old Win 7 hdd there is another folder w same name Program Files.  There is no way Win 10 will go there to launch an application. afa Win 10 is concerned every folder on Win 7 hdd is pure data.  Mind you you also cannot copy paste Win 7 HDD Program files folder content into  Win 10 ssd folder. It would not work.  32 bit applications will also run into errors if you try to run it in 64 bit OS.
Better reinstall applications in Win 10 environments.

To a purist the Win 7 hdd data (doc, photo, video) should be backed up on external hdd, then hdd wiped as a fresh clean data drive.

Never mind the other link, this is closer to what I was looking for.  https://www.dell.com/support/home/en-us/drivers/driversdetails?driverid=nwjxj 

Hardware identifying info will be on Win7 HDD.  When it's placed into a different PC, it'll detect "new hardware" and ask for restart(s).

You may have to download new drivers - chipset, graphics, etc.  https://www.dell.com/support/kbdoc/en-us/000121578/optiplex-7010-windows-7-driver-cab 

When I moved Win7 HDD from a 755 to a 790, I used Dell Support Assist to scan PC for necessary drivers.  I don't know if you can still do that due to lack of support for Win7.

Be sure to keep security current on Win7 drive.

There really shouldn't be too much trouble with the transfer, especially if the drive is coming from another Dell PC.

Anything Microsoft will likely ask for reactivation.

Thankyou for all the info.

You're welcome.  : )

The only other thing I wanted to add is if previous Win7 PC didn't have USB 3.0, you'll need a driver for it.  You might already know - Win10 has USB 3.0 built in.

 "32 bit applications will also run into errors if you try to run it in 64 bit OS."

Quite true.  32-bit apps/programs simply won't work on 64-bit OS.  I inadvertantly tried it myself and keep Win7 32-bit on a separate PC.