If you want to add/attach file to the items of the application through workflow, here is the flow setup to get this working:
Step 1: Event
Click on "+Add Step", select "Event" and then "+Add".
Select the target application, event type (the flow initiates as per the event selected e.g. if "When item is created" is selected, the flow will initiate when item is created) and the filter conditions (optional).
Step 2: PDF
Click on "+Add Step" ,select "PDF" and then click on "+Add".
Set the options for creating the PDF file. Set the Page layout using the “Layout” setting, page size using the “Size” setting. Page margins for PDF are set to a default value of 10 mm and they can be modified if needed by using the page margin settings.
Step 3: Update Item
Click on "+Add Step" ,select "Update Item" and then click on "+Add".
Type in the values in the field in case you want to update any field and checkmark the PDF page option from "Attach file/s from step".
Step 4: Workflow Type
The workflow will execute as per the workflow type selected. As we have selected "Immediately on app item events like create, update" so the flow will executed immediately on item create, update provided that the filters condition matches.
Step 5: Save> Test> Publish
Save the workflow after all configuration by clicking on the Save button ,Test it and Publish the workflow.