Can you confirm that the file /opt/tomcat/temp/axelor/Nursys-QuickConfirm-License-Verification-Report_2019_01_18 (1).pdf exists ?
Each file (picture in Partner, DMS, etc…) are upload inside the folder defined in the application.properties using the property file.upload.dir. In your case it seems to be {java.io.tmpdir}/axelor (the default value). As its name, this is a temporary folder which is not the best choice to store non volative data.
Check if your folder /opt/tomcat/temp/axelor still exists and that it contains your documents.