Erasing first gen (I think) MacBook Pro

Grant Bennet-Alder wrote:

On an Intel-based Mac, if you use Shift-Option-Command-R during startup, you might be offered the macOS that came with your Mac, or the closest version still available.

FYI, for a 2007 or 2006 model, this key combination was not available. The closest option (besides Command + R) that may be available is Command + Option + R which is supposed to allow reinstalling macOS 10.7+ without requiring an AppleID to verify "purchase" and to prevent the clean OS from being associated with the previous owner's AppleID. Unfortunately Apple's documentation is not entirely clear and is very limited.

"you can't cut off the branch you are standing on".

Tto erase the drive, the approved method is to do so from Recovery, so that you can, in the same session, re-install the oldest available version of MacOS available online:

On an Intel-based Mac, if you use Shift-Option-Command-R during startup, you might be offered the macOS that came with your Mac, or the closest version still available.

What to do before you sell, give away, or trade in your Mac - Apple Support

How to reinstall macOS - Apple Support

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If this laptop is using a hard drive and Filevault was not enabled, then you would want to write zeroes to the entire hard drive in order to overwrite all your personal data. If you don't have the OS X 10.6 Snow Leopard DVD installer, then you do have the following options to securely erase the hard drive.

If this is a 2007+ MBPro, then you can create a bootable macOS 10.11 USB installer. If this laptop is unable to boot into local recovery mode and you have access to another Mac from 2008 to 2015, then you can use this other Qualifying Mac.

Create a bootable installer for macOS - Apple Support

While booted to the 10.11 USB installer, you can use Disk Utility to write zeroes to the hard drive while erasing it, then afterwards you can install macOS 10.11 (for a 2007+ model only).

If you have a 2006 model or don't have access to another Qualifying Mac, then another option to securely erase the hard drive is by creating & using a DBAN CD (must burn the .iso file contents to CD, not just the DBAN .iso file) or the newer ShredOS which can be booted from a USB stick (you need the .img file for the latter). You can used the downloaded ShredOS .img file as a source for Etcher (Mac/Windows/Linux) which will make a shredOS bootable USB stick.

Another option if you would prefer to keep using this laptop at least for basic tasks such as getting online to browser websites or accessing email and such, then you may want to consider installing Linux Mint to this laptop. Linux works well with 4GB of memory, but can be used with as little as 2GB of memory. Linux provides you with a current up to date non-Apple OS with access to the current versions of popular web browsers (Firefox, Chrome, Vivaldi and others), plus access to lots of free open source software in the Linux distributions software repositories like LibreOffice. Of course Linux is not for everyone and it does require learning a new OS, but it is a great way to extend the useful life of older computers.

If you decide to try Linux Mint, then make sure to prepare for it. First make sure you create a bootable macOS 10.11 USB installer if you have a 2007+ model so if you decide Linux is not for you that you can reinstall macOS to the laptop. Second, in order to use the built-in iSight camera with Linux you may need to retrieve the iSight camera firmware file from your current macOS installation which may be needed by Linux.

The only time I do not recommend Linux on a Mac is with the 2006 MacBook Core Duo model with the 32 bit CPU since that particular model laptop has really buggy firmware and won't work correctly, plus most Linux distributions are dropping 32 bit support. AFAIK, the 2006 MBPro should be fine since it has a Core 2 Duo CPU.