Hi Sunnyl,
As you have mentioned above, you have downloaded the latest AcroRdrDC_1801120035_MUI.dmg file on your Mac book air.
It seems that you referring to AcroRdrDC_18001120036_MUI.dmg file. It is a patch installer file for Reader DC.
You will be able to install recent patch only if you already have the prior version installed on the machine.
Please refer this help document Release Notes | Adobe Acrobat, Reader to check the updated patch list.
Could you please check the version of the already installed Reader DC?
You can use the steps mentioned here Identify the product and its version for Acrobat and Reader DC to check the application version.
If you still experience the issue in installing the patch, you can refer the steps mentioned below to install the latest version.
Run the cleaner tool Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs on Mac and reboot the machine.
Then download the Adobe Acrobat Reader DC installer file from here Adobe - Adobe Acrobat Reader DC Distribution.
Once the application install, launch the application and go to Help > Check for updates. It will update the application to the latest patch available.
Hope that helps.
Let us know if you experience any issue.
Regards,
Meenakshi
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