We're sorry for the delayed response and inconvenience caused. As per the description above, you are not able to convert a PDF file when the firewall is enabled, is that correct?
The record shows that you are subscribed to Adobe PDFPack services, Is it possible to connect the machine to a different network environment like a guest wireless network or a mobile hotspot and then try converting the PDF file through the URL https://cloud.acrobat.com/convertpdf with your Adobe ID and password on a different browser.
For testing purpose, user your mobile device on the cellular network and try converting the PDF file.
Is it a personal computer or an office computer? Is any security software is installed and what is the version?
I have also shared the Adobe list of Ports and URLs by private message, you have to whitelist them on the network and firewall. Please check your email inbox.
For more troubleshooting, you may refer to Troubleshooting Create PDF, Export PDF, Adobe Send, Fill & Sign … services(PDFPack or Document Cloud...
let us know how it goes and share your observation.