When filing by mail you are required to attach an original copy of any W-2s that you have. What exactly “original“ means is more tricky these days. In the past, a W-2 was a multi part carbon paper form. The top copy or copy A, was sent to the IRS by the employer. The second best copy, copy B, is what you were supposed to attach to your tax return and send to the IRS. The copies behind copy B, which were of lesser quality, were for your records or for state income taxes.
These days, your W-2 is likely to be a single sheet of paper that has four copies computer printed and then it is folded and the edges are glued. Even though all the copies are of identical quality, one of them is labeled “copy B to be filed with your federal tax return“ and you should include that because that’s what the regulations say.
In some cases, you might opt to get your tax documents electronically from your employer in which case your W-2 is a PDF with 4 copies of the w-2 on one page, but even then, one of them will be labeled “to be filed with your federal tax return.“