Hi Magdalena,
Thanks for your interest in Syncfusion products.
HTMLUI Control's 'LoadFromString()' method is used to load the HTML code available in the form of string and the HTML contents will be displayed in the HTMLUI control. For more information i have included the Documentation link for the same as follows.
[Documentation]
http://help.syncfusion.com/ug_93/User%20Interface/Windows%20Forms/HTML%20UI/Documents/4124loadinghtmlwhichisintheformoftext.htmAnd currently we do not have support to return the number of lines of the HTML contents displayed in the HTMLUI control.
Please let us know if you need any other details.
We are glad to assist you.
Regards,
Iniyen M.A.