NightPDF is a free and open source PDF reader application for Linux, Windows and MacOS. Using NightPDF, you can change your PDF file font color, background color, adjust darkness, gray scale, sepia, hue, brightness and inversion. It comes in pre define dark, Sepia, Redeye modes and you can also set custom colors for your pdf. It is released under GNU General Public License v2.0.
Install NightPDF on Ubuntu Linux
NightPDF is available as a portable AppImage and flatpak package file. Download NightPDF in .AppImage file format from the above link and save it on your Downloads folder. Open the terminal software (ctrl+alt+t) and run below commands one by one. Here “NightPDF-0.4.4.AppImage” is the downloaded file name . You can change below command based on your downloaded file name.
sudo chmod +x ~ NightPDF-0.4.4.AppImage
Install NightPDF via flatpak:
First install flatpak and flathub on your system and restart it after the installation. Now open the terminal app and run below NightPDF flatpak install command.
How to install flatpak and flathub
flatpak install flathub io.github.lunarequest.NightPDF
And open NightPDF app using below command.
flatpak run io.github.lunarequest.NightPDF
And uninstall NightPDF using this command.
sudo flatpak uninstall io.github.lunarequest.NightPDF