How can I control whether the last file opens when I start the software?

When the software starts, you have the option to either have the last file load automatically or to open to the File Manager.

You specify this option in the File Manager on the Settings gear as shown below.

If this option is checked, then, when you open the program, the last file you were working on will open up.

If this option is cleared, then, when you open the program, you will open directly into the File Manager and be able to select the file you want.