Character limit on text field for decimal number

What is the reason to not use the floatingPointField? You could use the round() function to modify the value on save.

as per requirement we have to use it in text field only

That's not a real reason, but here is a example that you should adapt to your exact needs.

a!localVariables(
  local!value,
  {
    a!textField(
      label: "Decimal",
      value: local!value,
      saveInto: a!save(
        target: local!value,
        value: text(round(todecimal(save!value), 5), "#.#####")
      ),
    )
  }
)

Thanks Stefan 

but its works up to certain limits like if I enter 14 digits before decimal then its not working, values after decimal are changing.

You did not mention the range of digits you need. You will have to adapt line 9 to fit your actual requirements.

a!localVariables(
  local!value,
  {
    a!textField(
      label: "Decimal",
      value: local!value,
      saveInto: a!save(
        target: local!value,
        value: a!localVariables(
          local!parts: split(cleanwith(save!value, "0123456789."), "."),
          concat(
            local!parts[1],
            ".",
            left(index(local!parts, 2, "0"), 5)
          )
        )
      ),
    )
  }
)

Thanks Stefan

and one thing if I enter any text or special character it should throw an error is it possible with this code because it is storing numbers only

You can add a validation in the textfield like:

validations: if(
    todecimal(local!value) = local!value,
    {},
    "Characters are not allowed"
)

My example already removes any non-digit character.