Hi slpera
You are wise to inquire before attempting to download or open files that you receive over the internet, even when those file attachments "appear" to be coming from a friend or relative.
I would speculate that your daughter may be attempting to complete some form of Student Aide or may be involved in a branch of the military that requires this type of document format. I would certainly call the person by telephone to confirm that the document was sent by them
The link provided by Appleoddity does a good job of describing what xfdl format documents are used for.
More information can be found at Grants(dot)gov
Getting to the actual reader-utility required by government grant and other sources can be somewhat of a tail-chase, jumping from site to site.
Again the link provided by Appleoddity does offer a Download, but it may be more than you want, and certainly is more than you need to open XFDL formatted documents.
You can download and install a specific application called PureEdge Viewer, directly from
http://www.grants.gov/agencies/asoftware.jsp
Here's a screenshoot - the Red line points to the clickable link to begin the download of PureEdge Viewer
📎PureEdge_Viewer_requirement_n_download.jpg
I do quite a bit of correspondence with government agencies, but this XFDL file format was a new one for me.
Therefore I decided to investigate, download, and create a trial download of PureEdge Viewer.
I first created a New Restore Point. (I already have a full back-up of my Registry)
Just in case something went wrong or conflicted when installing.
Installation of PureEdge Viewer from grants.gov page linked above went just fine without a hitch on this test machine running (laptop running XP professional, but should work just fine with XP Home as well)
That's about as far as I can help.
Now I just need to acquire an XFDL document to open.