If you've purchased Adobe Acrobat Xi Pro 11.0 20, you can find the serial number in several places:
You can buy Adobe Acrobat XI Pro directly from Adobe's official website. Adobe often provides a serial number or a download link where you can purchase and download the software directly. Adobe Acrobat Xi Pro 11.0 20 Serial Number
Search your email inbox for the purchase receipt from Adobe or the retailer (e.g., Best Buy, Amazon). The email usually contains the 24-digit serial number. If you've purchased Adobe Acrobat Xi Pro 11