I knew sentences like "Is this your pen?", "This pen is yours", "Your pen is beautiful", but I don't see sentences like "This your pen is beautiful". Can I say that?
It's not correct English as you intend it.
"This" and "Your" are determiners, and specifically referring determiners. And you only use one referring determiner at a time.
This my pen
My the pen
The this pen
This can also be a pronoun, meaning "this thing". It could be used as :
This, your pen, is beautiful.
to mean "This thing is beautiful (this thing is your pen)"
The use of "this" or "yours" as pronouns, not determiners allows: "Is this your pen" (understood as "is this thing your pen") and "This pen is yours" (understood as "This pen is your thing")
Instead, maybe you could say: "This pen of yours is beautiful".
To elaborate on the good answer already, in English there is no need to give a determiner or pronoun ("This") as well as a noun or noun phrase itself ("your pen"). It isn't usual, and doesn't normally add anything; it sounds like what it usually is - an attempt to use grammar from a different language, and foreign to English.
Instead you would either say "This/That is beautiful" if it's clear what you refer to, or "Your pen is beautiful" if it is not clear, or you want to be sure they understand the specific object you mean.
The one time you might use both is exactly the example given in a previous answer. This is not often used, but would be used when you wished to really emphasise something, much more than usual. For example, if you visited a friend's town or family for the first time and you were completely overwhelmed by the beautiful countryside, or the wonderful family, or maybe if you were writing: This - your countryside - is beautiful!.
If the sentence avoids using both a determiner (or pronoun) and a noun (or noun phrase) for the same object, the awkward wording is not a problem. So alternatives like these are closer to ordinary use as well:
"That pen, the one you showed me, is beautiful", or "That - the pen you sold - is beautiful". In these examples, the second part clarifies which exact object or pen "That (pen)" is referring to.
"This, your signature, shows you agreed to the contract" - here it's also clarifying the object referred to by "This". It also slightly emphasises the object as the focus of your sentence: "This, meaning your signature, ....."