Navigate to Settings > Customization
Go to Report to PDF Setting and click on Fields.
Create a new field with name as new_fieldname and Schema Name as new_Fieldname
Go to Form and add the newly created field
Go to Advance Find and select Report to PDF.
Open any of the previously configured entity. For example, account entity here.
Enter Schema Name in Field Name as shown in the below image
Note: Take Schema Name as String Field only.
Go to Sales > Accounts. Select any record and perform Report to PDF functionality.
Click Open PDF button
You will notice that the field value is assigned to the PDF file dynamically irrespective of what field name is given in the above image. In case where the field value is not given, the above field name will be assigned to the PDF file.
This customization also works on Attach to Notes, Attach to Email and Save as Excel.