What is a CXF File?

How to Open, Edit, & Convert CXF Files

CXF file

A file with the CXF file extension is probably a Picasa Collage file. They're created by the Picasa photo editor and organizer program when a collage is built, and then saved with the image files. The CXF file retains the paths and positions of the photos used in the collage.
Chemical Abstracts Exchange Format files that store molecular data use the CXF file extension as well.
Other CXF files may be Cuttlefish Extended Format files, Coordinates Export Format files, or Color Exchange Format files.

How To Open an CXF File 

Picasa Collage format CXF files can be opened with Google's Picasa. This type of CXF file is actually just a text file, so any text editor can open it too if you need to see the image paths and other things that are stored within the file itself.
If your CXF file is a Chemical Abstracts Exchange Format file, CAS SciFinder and STN Express can open it.
Some CXF files store values for a graph used with the Cuttlefish network visualization tool, in which case that program is used to open them.
Use CXeditor if you need to open a CXF file that's a Coordinates Export Format file.
If you think your CXF file is a Color Exchange Format file, you can read more about them at X-Rite. Files in this format are XML based files that store things like color measurements. You can open one with any text editor or XML viewer, Notepad++ being one popular example.
Note: CXF files look awfully similar to files that have the XCF, CXD, CVX, or CFX extensions, but they have nothing to do with one another.
If you find that a program on your computer is the default one for CXF files, but it's the wrong application or if you would rather have another installed program open CXF files, see my How To Change the Default Program for a Specific File Extension guide for help making that change in Windows.

How To Convert a CXF File 

I have no doubt you could convert a Picasa Collage file to another text-based format if you really wanted to, but I can't imagine a reason to do so.
The CXF file explains how the collage should appear in the Picasa program, so changing it to any other format would render the collage unusable.
I haven't tested it myself, but I'm sure that a program like CAS SciFinder or STN Express can export a CXF file to a different format.
The same goes for Cuttlefish - most programs have an Export or Save as menu item that can be used to save the file to a different format.
CXeditor is able to export a Coordinates Export Format CXF file to SVG, KML, EMF, AI, or XAML.
If your CXF file is a Color Exchange Format file, you can definitely save the XML-based file to another text format with Notepad++, but changing the format doesn't seem helpful here.