How can I prevent copy paste for a field like Account Number

It appears that Appian does not have any attributes that would apply to those things.

This kind of low-level customizations are not supported.

You can use Masked Parameter at that time it can prevent you from copying 

In Appian, if a field is "masked" that means its input is hidden like a password box and it doesn't prevent you from copying.

As other guys are mentioned, in Appian its out of box feature, even masking attribute can do like password box and not prevent copy and paste

Hello ghanashyamm0005,

Not something great but just for the time being you may try this simple logic.

a!localVariables(
  local!text,
  local!dummy: "************",
  local!reEnter,
  {
    a!TextField(
      label: "Password",
      labelPosition: "ABOVE",
      value: if(
        and(local!text, local!reEnter),
        local!text,
        local!dummy
      ),
      saveInto: local!text,
      refreshAfter: "UNFOCUS"
    ),
    a!textField(
      label: "Re-Enter",
      labelPosition: "ABOVE",
      value: local!reEnter,
      saveInto: local!reEnter,
      validations: if(
        exact(local!text, local!reEnter),
        "",
        "Values do not match"
      )
    ),

  }
)

This will do the work I guess.

encryptedTextField will take care of that

a!encryptedTextField() plus masked will prevent copy paste.