There could be multiple root cause for this issue like drivers problem, connectivity problem, compatibility issue, hardware issue or installation problem. Please try some troubleshoot option available in the link https://helpx.adobe.com/acrobat/kb/troubleshoot-scanner-issues-acrobat.html. Note: Acrobat Pro 11 is already declared as End of support product, End of Support means that Adobe no longer provides technical support or distributes runtimes. This policy affects product and security updates for all derivatives of a product or product version (localized versions, minor upgrades, operating systems, dot and double-dot releases, and connector products). For detailed information, please refer to End of support for Adobe Acrobat XI and Reader XI
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