I have to upload 5 (min and max) .txt  files at a time, I'm trying to validate throught JS the minium or max number of files and send a message, but with the validation events that are there i can't actually do that. Is there any other way? Or a way to create a custom validation for uploading files?

Hi Juan,

You could subscribe to the upload or select event of the Upload widget and check the count of the files. In case the files are more or less than it is required, you could prevent the uploading. Please refer to the following thread from our Forum where such issue is discussed:
- https://www.telerik.com/forums/how-to-restrict-the-number-of-files-for-a-single-upload

I hope this helps.

Regards,
Neli
Progress Telerik