Re: RNDP 4000 Readycloud
Is there any way can use the readycloud with RNDP4000 NAS Device?
The only way is to convert it to OS-6. The Pro can be converted, the NVX can't be. So it's important to use confirm the model. Conversion requires reformatting all the disks, so you'd need to have a full backup of the NAS. Netgear doesn't support that configuration (so you'd lose access to paid support). Still, many people here have done the conversion successfully. Consider upgrading the RAM in the Pro if you go down this path - currently shipping OS-6 NAS have at least 2 GB of RAM, while a stock Pro only has 1 GB.
You could run OwnCloud on the Pro as it is, and that has similar features. There's a convenient package you can get for a small cost here: https://rnxtras.com/readynas-os4-x86