Final Draft 7 cannot export as PDF in Windows 10 / 8 / 7. Users of FD7 will want to consider the upgrade to Final Draft 10, which was designed for these systems and has no problems exporting PDFs. Information on the ugprade is HERE.
These steps might work:
If this works, remember to go back to Start > Computer > Tools > Folder Options > View Tab, check Do Not Show Hidden Files and Folders and then click OK.
NOTE: All support for Final Draft 7, including software activation, has been discontinued. You may find solutions to problems in the online knowledge base or in the PDF manual found on the installation CD.