I copied this stuff from an ATF publication. Eform news volume 2, issue 1. It outlines file formats supported and size of attachments for efiling.
When adding attachments make sure that the attachment you are attempting to add is one of the acceptable attach- ment types:
a. Word (.doc, .docs, .docm)
b. Portable Document Format (.pdf)
c. Excel (.xls, .xlsx, .xlsm)
d. PowerPoint Presentation (.ppt, .pps, .pptx, .pptm)
e. Joint Photographic Expert Group (.jpeg, .jpg)
f. Graphic Interchange Format (.gif).
Attachment Limitations
The maximum size of a single upload for an attachment is 3 MB and the total size of the attachments cannot exceed 30 MB (with a maximum number of attachments of 10 at- tachment for the Forms 1, 2, 3, 4, 5, 9, and 10). Forms 6 and 6A may contain a maximum of 10 line attachments per line item (the total submission cannot exceed 30 MB per sub- mission).
Instructions NFA Trust Documents:
We have been advised that, for NFA forms, the size of the trust or corporate documents may exceed the 3 MB limit. If you encounter this situation, we suggest that you split the document into 2 or more ‘packages’ (as needed). When the attachments are added, identify the packages as, for exam- ple, ‘XXX Trust 1 of 3,’ ‘XXX Trust 2 of 3,’ etc.
Note: After you submit the application attachments cannot be added.