My download manager does not show files on the Voice Tracer 7780. I am working with Windows 7. Is there any software existing for transferring MP3-files from my PC to the Voice Tracer?
If you don't have the software, the device should be available for connection in MTP mode which allows you to browse the contents while it's attached to PC without the need to have the software installed.
I've checked their Support page, but there isn't anything available about this version you have. I recommend to contact them using the available options: https://www.dictation.philips.com/us/support/contact-philips-dictation-solutions/
They should provide the necessary info.