Allowed file type(s)
The Allowed file type(s) property allows you to specify the file types that the user can upload using the File field. Once you set the permitted file types for a field, users will not be able to upload any other file types apart from the ones mentioned in this property.
For example, if you set the values for this property as "pdf, png, md," the user will only be able to upload files PDF documents, PNG graphic images, and Markdown files on the entry page.
Additional Resources: Validations let you eliminate errors while writing content. You can check out the Validations guide to know more.
Making changes in existing field properties may result in data loss. To prevent this, make sure you go through our Content Type Change Management guide before you go ahead.