Here is the basic file upload field type: https://github.com/tamagokun/acf-basic-file
One problem I ran into was that the form needed to have it’s enctype set, which I did at the time with the class name of the form. To make this more universal I changed it to try to find the parent form element of the field. Didn’t test it though, so you may have to change this line: https://github.com/tamagokun/acf-basic-file/blob/master/basic_file-v4.php#L268
I used that field type in conjunction with a plugin I wrote specifically for creating dynamic front-end forms using ACF: https://github.com/tamagokun/acf-forms
