why can't I open Word document on my new apple laptop after I transferred it from my apple desktop?

You may need to reinstall MS-Office (or Word) on the new computer.

Or your version may be too old to run on it. The Office 2011 suite is too old to run under the latest operating system. It is 32-bit based and you need the newer version that is 64-bit.

You can also open your Word document using the Pages program that came installed on your new Mac. Pages can also save documents in MS-Word format. You can use this while deciding if you want to purchase the newer version of Word or Office. You can purchase a standalone version of Word or Office that installs once on your Mac, or a perpetual version (Office 365) that requires a monthly fee.