Hello Hannahm,
We apologize for the inconvenience caused, as per the description above, you are not able to open a PDF file, Is that correct?
Please check for any pending updates of Adobe Reader from help>check for updates, reboot the machine after updating Adobe Reader and see if this brings any difference.
Are you not able to open all the PDF files or is it specific to one PDF? If it is specific to one PDF file, Is it possible to share the PDF file with us? To share the file, please use Adobe Send feature, upload the file, share the link to files via private message only, How Do I Send Private Message
What is the dot version of Adobe Reader installed? To identify refer to Identify the product and its version for Acrobat and Reader DC
Is it a Mac or Windows machine and what is the version of OS installed?
If Adobe Reader is still freezing after installing updates, please use Acrobat cleaner tool to remove Adobe Reader Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs
Reboot the machine and install the latest version of Adobe Reader from Adobe - Adobe Acrobat Reader DC Distribution
Let us know how it goes and share your findings.
Regards,
Anand Sri.