Hope you are doing well and sorry to hear that. As described it takes lot of time to load the PDF and after loading its not clear.
Would you mind sharing the version of the Adobe Acrobat DC you are using? To check the version go to Help > About Acrobat and make sure you have the latest version 21.05.20048 installed go to Help > Check for updates and reboot the computer once.
Id this a behavior with a particular PDF file or with all the PDFs, Please try with a different PDF file and check. if the file is stored on a shared network/drive please download it to your computer first and then try to open with Acrobat/Reader DC and check.
Are you on Mac or Windows Machine and what is its OS version? Please check for any missing/pending updates and try updating it and check.
Also, go to Edit (Win), Adobe Acrobat (Mac), > preferences > Page Display > Under rendering, Uncheck 'Use page cache' > Click OK and check