This function s used to merge multiple PDF files into one one.
Select SET command from the action dropdown and provide a variable name in Element key where output will be stored, edit parameter section and click on Form, select functions from the dropdown and select PDFHANDLE function and then choose action as pdfmerge. Provide path of pdf file for destination in which all other pdf files will get merged and provide multiple pdf files path that you want to merge.
After merging all the pdf files with the one defined in destination, it will return the path of destination pdf file in a variable defined in Element key. After completing the step it will look as below: