Ton of info on Wikipedia...
The name is VALDemar, not VLADemar, so that might be confusing your searches.
The movie you are talking about is "Eye of the Eagle" and it is a Danish production made in 1997:
https://en.wikipedia.org/wiki/Eye_of...gle_(1997_film)
Valdemar II (the Younger's father) is a hero of Denmark, so there is a decent amount of information about him. Wiki has a page on the father and the son:
https://en.wikipedia.org/wiki/Valdemar_II_of_Denmark
https://en.wikipedia.org/wiki/Valdemar_the_Young
The wiki page contains a source list and one of them is a link to a page on Valdemar the Younger that contains a list of medieval texts in which he is mentioned and his story is drawn from:
DENMARK KINGS
I would suggest searching for info on Valdemar II and you will find a lot of info. The Younger's story is inextricably tied to that of his much more famous father since they ruled together and the son died first.