Upgrade HDD to SSD

You don't have to take the source HDD out before cloning.  You can attach the target disk via USB, run the clone from within Windows, and then shut down and install the target internally to boot from it.  Another option would have been to run the clone from within the Acronis bootable environment rather than within Windows.  The reason your described method of moving the source disk to USB first and then trying to boot from it didn't work is that Windows does not support being booted from a hard drive that's connected via USB -- never has.  The only exceptions are Windows To Go, which is a custom setup that also requires enterprise licensing, and Windows PE, which is what Windows Setup and the Startup Repair / Recovery environment uses.  Some other tools build their bootable environments on Windows PE, including some cloning/imaging tools like Acronis.

I have no idea why BitLocker is appearing all of a sudden if you didn't enable it.  It sounds like either there's another device or partition visible to the system that does have BitLocker enabled, or perhaps your company domain enforces a policy that enables BitLocker.  Note that the default BitLocker mode does NOT require entering a PIN at every boot; it just unlocks using a key stored in the TPM, so it would be easy for BitLocker to be enabled on your OS partition without you realizing it -- but once you change to a different hard drive, you would have caused the system to fail the "platform integrity check", which would prevent the TPM from releasing the key and prompt you for a recovery key instead.

Have you considered just asking your company's IT department to help with this?

In addition to the above, if I'm right about BitLocker having been enabled on your OS partition, perhaps due to company policy, then you have a few options for how to proceed.  The first order of business would of course be to regain access to your system.  You should be able to do that by simply reinstalling the original source drive internally, disconnecting the target and trying to boot the system, since that will return the system's hardware profile to what's expected by the platform integrity check, and allow Windows to be booted from that drive again since it won't be attached via USB.  Then open up your BitLocker settings and see if your OS partition has in fact been encrypted.  If so, choose to back up the Recovery Key and store that somewhere that you'll be able to access without using your PC, such as your smartphone or email.

If your OS partition is encrypted with BitLocker, you have two options for how to proceed with the clone:

- Run the clone from within Windows by having the target connected via USB, and then installing it internally after the clone completes in order to boot from it.  This will cause the target to be unencrypted, since the OS partition is unlocked when you're running Windows.  As a result, if BitLocker was enabled by a company policy, it will probably be re-enabled again on the new drive eventually, in which case keep an eye on that and back up its new Recovery Key after it happens.  OR....

- Run the clone from within the Acronis bootable environment.  This will cause the target to be encrypted since the source partition will be locked in this environment; this method will also take longer because the entire partition, including unused free space, will have to be cloned, because while a partition is locked, Acronis can't tell which parts of the drive contain meaningful data and which parts are unused.  After the clone completes and you install the SSD internally, you will very likely be prompted for the Recovery Key due to the hardware change.  Enter the Recovery Key that I suggested backing up earlier, and at that point the system will "reseal" to the new hardware profile, and you should then be good to go.