Problem

BACK4 may create bad (very grany or very low resolution) PDF previews.

Cause

Insufficient resolution of the preview, due to the workflow settings.

Solution

If you are using older versions of workflow, consider to upgrade to newer, or to change your existing workflow to create a better preview. See the information related to GN4-1897 in Changes of workflows in the version 2.0.

If this doesn't help, consider the below workaround.

Workaround

Stop the Back4 service, restart it and then reprocess all PDF files with bad previews