Follow these steps:
1- Check for updates, launch Acrobat>navigate to help menu>select Check for Updates. If there is an update available, download and install it and then relaunch Acrobat.
2- If that doesn't work, select Edit menu>Preferences>Page Display>Rendering>Smooth Text>select None from the drop down options>OK
3- Relaunch Acrobat.
Also, if there's a lot of text, pictures, or images, try compressing the file by following these steps:
1- Open up Adobe Acrobat
2-n Open the file.
3- File --> Compress PDF
4- Follow the prompts