The file is a compressed archive created using 7-Zip. Because 7z is a generic container format, the specific contents depend entirely on who created it.
Scanned copies of tax returns, W-2s, 1099s, or receipts. tax2.7z
Right-click the file and select 7-Zip > Open archive . Command Line: Run 7z l tax2.7z (the l stands for "list"). On macOS/Linux The file is a compressed archive created using 7-Zip