Software & Apps File Types What Is an SZN File? Share Pin Email Print File Types Design Cryptocurrency MS Office Windows Linux Google Drive Apps File Types Backup & Utilities View More By Tim Fisher General Manager, VP, Lifewire.com Tim Fisher has 30+ years' professional technology support experience. He writes troubleshooting content and is the General Manager of Lifewire. our editorial process Facebook Twitter LinkedIn Tim Fisher Updated June 10, 2019 A file with the SZN file extension is a HiCAD 3D CAD file. SZN files are used by the computer-aided design software called HiCAD to store 2D or 3D CAD drawings. The SZN drawing format is used by older versions of HiCAD, while newer versions of the software use SZA and SZX files. How to Open an SZN File SZN files can be opened with ISD Group's HiCAD. The program isn't free to use but there is a demo you can download that should also provide the same support for these files. The free HiCAD Viewer, also from ISD Group, can open SZN files too, but only if they contain shaded 3D models. This means 2D models or glass models that are saved in the SZN format can't be opened with the viewer. On the HiCAD Viewer download page is two options for each version of the program. You can get the 32-bit or the 64-bit version, and your choice depends on the type of computer you have. It's easy to figure out which version you need if you're not sure which link to choose. If you're also working with some other file types used with HiCAD, you should know that this free viewer program can open 2D drawing files in the ZTL format, plus SZA, SZX, and RPA files, as well as HiCAD Parts and Assemblies files in the KRP, KRA, and FIG format. If you suspect your SZN file has nothing at all to do with the HiCAD software or CAD drawings in general, try opening it with a free text editor. If the file is full of just text, then your SZN file is just a text file that can be used normally with any text editor. If most of the text is illegible, see if you can pick out something identifiable from the mess that can help you research the program that created your file; it's usually also the same program that can open it. If you find that an application on your PC does try to open the SZN file but it's the wrong application or if you would rather have another installed program open SZN files, see how to change the Default Program for a specific file extension for making that change in Windows. How to Convert an SZN File The HiCAD Viewer software mentioned above can save open files to a different format. It's likely that you can use that program to convert the SZN file to some other similar CAD-related format. The same goes for the full HiCAD software. I'm sure in either the File or some sort of Export menu is the option to convert the SZN file. Most common file formats can be converted using a free file converter, but if you follow through with this link you'll find that none of the online services or converter programs support this SZN format. Still Can't Open Your File? If your file won't open as described above, there's a good possibility that you're just misreading the file extension and confusing a different file for one with the SZN file extension. For example, the SZN file extension is very similar to SZ used by the Winamp music playing software as a custom interface, or "skin." The two formats have nothing to do with each other even though it's easy to mix up their file extensions. If your SZN file doesn't seem to be anything related to HiCAD, it's possible it might be an ISZ (Zipped ISO Disk Image) file that you've mistaken as an SZN file. They're not related at all, format-wise, but do resemble each other on first glance. If you discover that you don't have an SZN file, research the real file extension to see which programs can be used to open or convert the file.