I have following html code:
<p><strong>Lorem Ipsum</strong> je fiktívny text, používaný pri návrhu tlačovín a typografie. Lorem Ipsum je štandardným výplňovým textom už od 16. storočia, keď neznámy tlačiar zobral sadzobnicu plnú tlačových znakov a pomiešal ich, aby tak vytvoril vzorkovú knihu. <em>Prežil nielen päť storočí</em>, ale aj skok do elektronickej sadzby, a pritom zostal v podstate nezmenený.</p>
After convert to pdf look this:

I try use word-wrap and also this: dompdf does wrong calculation for line breaks breaking words but not working for me.
In slovak language can not be "a" in the end of line. I need to have it like this:
"..tlačovín a typo-
grafie..."
or
"...tlačovín
a typografie..."
same problem in last but one with "v"
also we cant use numbers and century separately
"16.
storočia"
i need to have it like this:
už od
16. storočia, ... (together)
This problem can solve in html when i type 16.storočia without spacer.
Puuhh dompdf again - we use it on a drupal-project and this plugin made me angry several times. CSS2 and not CSS3-Support, no JS and buggy as hell!!
What you can do is putting the 16. storocia in a 16. storocia - This should keep them together. To the two other issues you have, try to wrap them in a span too.
It's not the best workaround but i think with typographic problems like these you'll always have to do all this "fine-tuning" by hand.
I hope i could help a little