avast false reporting?

When I scan my computer it keeps reporting ‘‘avast software\avast\pdf.dll’’ as malware.
What is causing this?

scan your computer with what?
and what does the report message say?

Scan the computer with Malwarebytes Anti Malware and the end scan reports states that the avastsotware\avast\pdf.dll within the installed Avast Premier programme is malware

So you have a program conflict / False Positive, this is not uncommon when having multiple security programs

You may report the false positive in Malwarebytes forum

False Positives > https://forums.malwarebytes.com/forum/122-false-positives/

you can also upload and check suspicious files at virustotal.com