So in short if I understand correctly, nothing has been infected, would have been the case if I opened the URL.
Possible, depends if the website that the URL point to is infected with something that could jump over to the computer, most likely that would also be detected, avast is usually good at detecting website malware
Avast detected the URL because it was blacklisted and in prevention of sorts put it in the chest.
Yes
Other AV vendors does it differently, they will let you read the pdf.doc but block the URL when you click it if blacklisted
I deleted them from the chest, if I'm right, this should delete the file from the pc permanently
Yes. Files moved to chest (quarantine) can not harm your computer, they are in virus prison, encrypted by the antivirus program and can not run
When you delete you dont have the option to restore it if it was wrongly detected ( False Positive )
Note that when you delete something in a computer it isn't actually removed, what you do is telling the operating system that it can overwrite that section on disk anytime it need to use that space