btw, @Carlos-Ugarte, welcome to the Magix Sound Forge users forum.
Try this, go to the "Options> Preferences> General" menu and enable (check-mark) "Always proxy compressed formats".
It is always best to work with PCM files, and encode an end user MP3 or other lossy formats when editing and/or mastering is completed.
FWIW, the new Pro-15 batch tool has the option to render and encode in multiple formats in one batch job. for instance if you need PCM, MP3 and AAC formats