A file with the PREL file extension is a project file for the Elements version of the video production and mastering software Adobe Premiere. Premiere Elements is a pared-down, beginner-focused version of the full Premiere program. Although it's similar to Adobe Premiere, Elements does not offer all of the options of the full version. However, Elements does include an Export feature that allows you to export an MP4 video from an Elements PREL project file. Only Premiere Elements itself can convert a PREL file to an MP4; you must have Premiere Elements installed on your computer to perform this conversion.
Open the PREL video project file in Adobe Premiere Elements.
Click the "Export" tool in the Premiere toolbox. The Export window opens. Alternatively, click "File" and then click "Export" in the File menu to open the Export window.
Click either the "H.264 (.mp4)" or the "H.264-encoded QuickTime (.mov, .mp4)" option for the export file type in the Export dialog box.
Type a name for the exported MP4 file into the "File Name" box. Type ".mp4" as the file extension.
Click the "Export" button. Adobe Premiere Elements converts the PREL file to an MP4.