Ans: Mail Merge Toolkit supports file masks. You can use those in a file path in a data source. As example: C:/Attachment/*.* to send all files from a folder, or C:/Attachment/*.pdf to send all PDF files.
Q: I need to send merged emails with a carbon copy
Ans: Additional CC and BCC fields are available in the settings to allow specifying secondary recipients.

Q: Can I preview emails before sending them?
Ans: You can use the Preview Results feature in Microsoft Word to check the messages before the sending. Also, a sending delay can be set to check created emails right in the Outlook Outbox folder before they leave it out.