If your report files are Excel, or delimited, and they all have the same structure, then open one Excel file, select a sheet, or open one delimited file.
In the preview screen, select table(s) and click on the Load selected table button. In the prep data screen you can modify data, such as splitting, adding a calculated field, adding filter, etc. Then click on the Add More stuff button and add additional Excel or delimited files to the data prep. Select the first table that you originally used in the data prep. On the right side, the change list, drag this button () and drop it to the other tables. The Data Prep applies all changes you made to the first table and applies those changes to the second table.
If your report files are text or PDF, first open one file in the Data Prep studio. Capture data in the report discovery page, the open it in the prep data. In the prep data select the table, click on the pick list, select Source Options, select Add File, and add additional files of the same structure to the prep data.
In the example below 3 PDF files are added, and the classJan object will display data for all 3 PDF files.
If you are familiar with the Monarch classic, the classJan table is similar to the table view, and each report under that table is similar to the report view.
This is similar to how Monarch works as well. You can only open one "database" at a time (access, excel, csv, etc.). If you want to open multiple excel files at the same time, you will need to add them to the workspace (right side of DPS) and then append them as needed. You can go the Preview data page (if you have multiple excel files in the workspace), select both sheets, and then select "Append selected tables". This will create a new table in the workspace (most likely called Append). You can then use the options Mo mentioned to select the button to drag and drop those changes on to the appended table.
To automate workspaces, you will need to create a visual process inside of automator.