Written
A file upload will add an input to your form that lets users select a file to be uploaded to the site server. ChronoForms lets you specify the allowable file types and sizes. This video shows you a simple example.
Please see this FAQ for more information on validating and debugging file uploads.
ChronoForms v5
The way you upload files in ChronoForms v5 is essentially the same. Add one (or more) File Field elements in the Designer tab; then add a Files Upload action in the On Submit event in the Setup tab. In the Files Upload action use the Files config box to set the allowed file types, and the Upload path to specify where the files should be uploaded to.
The HTML 'accept' attribute
If you want to specify the kind of files that are permitted before the file is submitted you can add the HTML accept parameter in the Extra Params box of the File Field element - you need to leave out the quotes round the value e.g.
accept=.pdf
