Hi,
If you are using HTML to PDF, then you can not have 100% height. The reason is the HTML to PDF converter will try to automatically detect your page height (so that it can determine how many pages the PDF file needs to be). This is exactly the opposite of how 100% height works --- in that case you have the browser window's height fixed first, then adjust the contents to fit the window. Fixing browser window height works fine on screen because it can add scroll bars. The HTML to PDF converter can not add scrollbars in the final output. So it must resize its "window" to fit the contents. If at the same time your contents resize to fit the "window", then it will create a dependency loop. So this will not work. You will have to change your HTML to avoid this.
One simple way to create full page content is to use the auto scale feature:
https://www.essentialobjects.com/doc/pdf/htmltopdf/auto_fit.aspx#autofitIf you set both AutoFitX and AutoFitY to ScaleToFit, then the converter will automatically scale the output to fit into a single page. That will achieve similar result as 100% height.
Thanks!