TempoWeave always saves your design as a standard WIF extension. This standard format is used for weaving designs downloaded from various internet site and all popular weaving software is capable of saving a design as a "WIF".
The following snapshot from file explorer shows a double-width blanket WIF that was created using a printed design published in the book, The Best of Weaver's - The Magic of Double Weave by Doramay Keasbey.
I like to save the names with "Master" in the naming when I am using section assembly to differentiate from the generated complete WIF.
Most weaving software has a proprietary extension, such as "DTX" in Fiberworks for their software. TempoWeave also has a similar extension of "TWA". Unlike other software, every time you save a design, the software saves both the "TWA" and the "WIF" file.
The TWA is actually a compressed file that contains the WIF, a file for the warp and weft structure assembly and the warp and weft color assembly.
The WIF is handy to use for copying to TempoTreadle or sharing with other weavers who may not have TempoWeave.
When opening a weaving design that has been previously saved from TempoWeave, open the "TWA" extension to be sure that you have the information from the section assembly and possibly other information that is not normally carried in the WIF.
In a folder on my PC in File Explorer, you can see my Master file (named with Master as a convention I use) and the generated design without "master" in the name (HerringboneBlanket). You need not worry about the TWA files. TempoWeave will always open the TWA if it's available. This documentation is only mentioned in case you are curious about the file names you observe in File Explorer.
If you happen to look in File Explorer while the application is open, you'll see a few more file extensions! These files should disappear when the program is closed. In case you are interested, these files can be opened with a text editor. The file with "wif1.waf" on the end contains the information on the warp ends from section assembly; "wif1c.waf" contains the color assembly for the warp ends. The file with "wif2.waf" has the information for the weft repeats and the "wif2c.waf" has the color assembly for the weft.