If the iPad was not centrally managed by a corporate MDM platform - and the employee was permitted to use their own AppleID - then the iPad will be locked to private AppleID account to which you will have no access.
You are therefore entirely reliant upon proving original ownership, to Apple. The original sales invoice that clearly shows the device serial number is usually required.
Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:
Activation Lock for iPhone, iPad, and iPod touch - Apple Support
Turn off Activation Lock – Apple Support
As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.