The first place to look is the Settings menu. There should be a View section where you can set default zoom options. If there isn't one, then simply close Open Text Imaging Windows Viewer and launch it again, but this time use Run as Administrator after right clicking on the launcher. This will give the software enough system access to store the settings. If you experience the same behavior after this, then the software doesn't support saving custom Zoom options.
For additional information, consult the official website of the software.
