If you used the Desktop program, the .tax files and pdf files are usually in My Documents in the Turbo Tax folder. Or search your whole hard drive for all files ending in .tax or .tax2018. And also look in the Recycle bin, people are saying they found it there. In the Desktop program you have to make sure to manually save it yourself, although it should ask if you want to save when you exit or start a new return. In Windows 10 they might be in the One-Drive area. Check your Recycle Bin and any other places you use or backup to like Drop Box or One Drive or any cloud backup services.
Find your Tax file in Windows
https://ttlc.intuit.com/questions/1900721-find-your-tax-data-file-in-windows
