Thank you for your post.
I am unable to replicate the issue using FileMaker Pro 13.0v3 on Windows 7. I have four records that contain a JPG image file, a movie file, a PDF file, and a FileMaker file. I created a button that executes the script step Export Field Contents with only specifying the Container target field. When I execute the script for each record, the suffix is included (.jpg, .mov, .pdf and .fmp12).
The only time I get an extension not to show is if I change my Control Panel -> Appearance and Personalization -> Folder Options -> View settings, and check the option "Hide extensions for known file types". Still, the file is saved without an extension showing, but the extension is saved.
Let me know what I'm doing differently so I can replicate the issue.
I believe I may owe you an apology. Our testing was with docx and xlsx files on a server that didn't have Office installed and we were relying on Wordpad to sub simple Word files. I've since checked using a PC with Office installed and, as you say, exported files are opening.
Please feel free to scratch this posting and sorry for (I believe) wasting your time.
First of all, I'm glad everything is working properly for you.
No need for the apology. The title of your original post is "Export Field Contents Loses File Suffix", and others may encounter the same issue. My reply includes the Control Panel settings that others may find useful.