you need to install linix headers generic by:

sudo apt-get update
sudo apt-get install linux-generic

I see you already have downloaded the realtek wifi drivers make sure you are in the right directory and run this to install them:

cd rtlwifi_new
sudo dkms add ../rtlwifi_new
sudo dkms build rtlwifi-new/0.6 
sudo dkms install rtlwifi-new/0.6
sudo modprobe -v rtl8723de ant_sel=2

Congrats you have running wifi.

Save the config with this command:

sudo /bin/sh -c 'echo "options rtl8723de ant_sel=2" >> /etc/modprobe.d/rtl8723de.conf'

Restart.

Details here:

https://h30434.www3.hp.com/t5/Notebook-Wireless-and-Networking/Realtek-8723DE-wifi-module-amp-Bluetooth-Linux-driver/td-p/6477307