Setting your book in LibreOffice Writer or Google Docs and then writing it to the .pdf format is obviously for downloading, printing and binding. For digital production it would seem that the options would be almost endless with all of the emphasis on e-Book delivery.
Unfortunately, that is not the case as most of the e-Book formats - e-pub and kindle dominate the market - do not support true fixed formatting conducive to works of photography. Although the .pdf format allows for text reflowing and some readers will adjust to the size of the device used for viewing the file this, is not the case with all readers. Setting the book in html using any of the advanced WYSIWYG editors can be a challenge especially when attempting to make the design responsive for the wide range of viewing devices.
The best answer is to set the book in an advanced content management system with a responsive template. Knowing that that system will handle all of the different displays and all of the different browsers will allow you to concentrate on developing your work.
The most popular content management systems are WordPress, Joomla and Drupal. While all three are excellent systems and can be used, the choice here is Joomla which combines the somewhat simpler approach of WordPress with the more control-rich environment of Drupal. Both Joomla and Drupal are complete systems but if Joomla has any advantage it is in the content entry system that gives the user a more familiar word processor-like system for entering content.
Joomla is offered as part of the hosting package of many ISP's and Hosting services, it is part of the Softaculous script installation service many hosting services use. It is available free through several web hosts including Cloud Access.net and Zettahost. Simply register with the site and you can start using the system. (Please note that there is no endorsement of any service here and no endorsement should be implied or assumed. Also note that web hosting services reserve the right to change their terms of services at any time and at their discretion.)
There is a learning curve with any content management system and there are a number of tutorials on the Internet that can guide you through specific questions and provide help when you need it.
But – these tips can help you get a Joomla installation set up for our purposes. Please note that these tips apply to an absolute box-stock installation of Joomla 3.8. There are no additional modules, plug-ins or templates used. Also note that Joomla is an advanced content management system and it will take a bit of adjusting to get it to work appropriately for your needs here. (This actually looks a lot more difficult than it is given all of the options in Joomla!)