Well, in the first instance, Avast doesn't know the password and thus would mark that pdf file as "suspicious" because it cannot open the file (it cannot know the password) and inspect it for malware.
This is important information not provided by you earlier in your original thread.
In the second instance, Avast may regard a pdf with attached files as also being suspicious, or worse, but again we cannot know what you see unless you post this information.
Suspicious or infected are two very different interpretations of a files cleanliness or malware state.
Attaching the actual virus alert will help us help you.
