To export form data from multiple PDF forms to a CSV file, please do as following:
1. Choose Form > Form to sheet > Combine Forms to a Sheet.
2. In the Export multi-forms to a sheet dialog box, click Add Files to add files that you want to combine into a sheet. You can also click Close button 
in the dialog box to remove files.
3. (Optional) Check the option Contain forms you closed recently to add the PDF files you closed recently. You can also append the exported form data to an existing file by checking the option Append to an existing file.
4. Click Export. In the Save As dialog box, specify a folder and file name (“data source.csv” by default) for the CSV file and click Save. A Foxit PDF Editor message will pop up to prompt that the form data has been exported successfully and let you decide whether to open the file.