Install Windows 7 on a new HP Laptop with Windows 10

Check on HP's site whether there are drivers available for Windows 7. If there aren't you'll have to expect that things won't work. If drivers are available, then there should be no problems in downgrading to Windows 7. Before you do anything, make sure you make a recovery USB stick from your current OS. For that open the control panel, select create recovery drive, and then make sure you select to also copy recovery partition. The stick needs to be just a little larger than the recovery partition is.

That way you can restore the system back to the original OS when needed.

"the new hp laptop" has some model number so others can check various HCL and driver sites.

No one has even tried to shed light on a "how to install 7 on this".
First, you need to see what model it is. It could be that the manufacturer has no drivers for win7 for download, so that 7 is out, unless the hardware component manufacturer himself offers a win7 driver. Check that.

Before you do this, you shoud tell us how you determined that these applications are incompatible. Normally, 99% of applications that run on 7 run on 10 as well. Exceptions are mostly softwares that use virtual device drivers like
-encryption softwares
-AV software
-firewall software

Remember: if some software manufacturer says "runs on 7 and 8.1", it does not mean it won't run on 10.It could mean, he never tested it on 10 and won't guarantee it. Or his statement is even outdated because he made it, before 10 was available.

It is usually same hardware but different licence embedded in BIOS. As we all know Windows 7 is upgraded to windows 10 for free. Say it might be that your windows 10 computer actually has Windows 7 or 8 activation code in BIOS.
Odds are high you are one windows update away from all drivers in case motherboard, if not try hp driver auto update.
If you dont have a single network driver obviously you need to carry that to system from other computer with internet.

Thanks everyone. I think the best way is to Install the VM for the legacy applications without disturbing my computer setup. It has good RAM, HDD and Processor, so it is not a problem.

Correct. And you will be able to use both Windows versions simultaneously without née to restart the system.

Thanks everyone. :-)

Best would be to get your software to run under the new OS. That should usually be possible, as McKnife already mentioned. Sometimes you may need to install some patches or updates, but it would make most sense. Only if that really isn't possible should you think of other options.

If the software really won't run under the new OS, a VM could be the best option, but you would still have to make sure your software runs properly within a VM. Some programs need direct access to hardware, and VM's can make that to fail. So this is something you'd really have to test.