Exploit.PDF-9669 was detected on older version of ClamAV.
Most HTML encoded email received seems to be matching on older version of ClamAV.
It seems to be a false positives matching on this signature.
Here is a temporary solution:
edit daily.hdb file
comment this line as below
and then restart the service
This problem will be solved for temporary.
I get this solution from this thread:
The permanant solution is
update your ClamAV to 0.95.3 and update your daily.inc or daily.cvd.