It can be defined beforehand what type of input may be made in the new field. Text: single-line or multi-line, date, numbers, numbers and decimals, email address, web address, selection list, checkbox, etc. If the new field is already filled in with a value, this can already be specified in advance.If the new field should be already filled in with a value, this can be specified also in advance.
Custom fields are always available and visible by default. However, if a particular field should only be available for one document type, this can be specified in the Administration. Simply select at "Show when this document type" the appropriate document type and save your settings. In the administration list, you can see for which document types which custom fields are used.