I am using DynamicReport to produce reports how to export

I’am using DynamicReport to produce reports. I can create the report, currently I export the pdf file to local disk.
How can I hock it on the ExportDisplay og add it to web context?

You can use ExportDisplay with ByteArrayDataProvider which is created for a byte array loaded from your file, as explained here. Alternatively, you can use SimpleFileDataProvider just passing the file name to it. In the latter case, your file should be located in the directories allowed by the cuba.download.directories application property (tomcat/temp/app-core or tomcat/logs by default).