Is it to copy score PDFs in order to gain experience/music theory knowledge?

What do you think?

At least study music scores. If you're new to this, choose a familiar and simple work, get hold of the score.

Step 1 is to try to follow it while listening to a performance; if necessary listen and follow line by line until you're pretty certain you are hearing each line properly.

Step 2 is try to read it in the absence of performance, If it's too difficult give more time to Step 1.

What you're aiming for here is to hear the piece in your mind while reading the score. It'll take time but without a performance to follow you can take as much time as you need. For some this is difficult. It takes perseverance. So go along bar by bar if necessary. If you think a couple of lines of a page is enough, move on to something else. This develops your inner ear that goes a long way to speeding up writing ideas that come to mind. It also helps you learn the different articulations of which an instrument is capable and how to notate them.

It isn't just what notes are played, it's how they're played that counts.

It may help to copy out some of a score. That would definitely make you aware of each line and copy the articulations. 

An orchestral score is more difficult but it's still the way forward: finding out how other composers have achieved their effects. If you intend to write orchestral music you need to know how instruments combine, what their strengths and weaknesses are so a textbook of some kind plus score study is the way to go.

But just as important is listening and working out what's going on. It was Gordon Jacob who said that good scoring comes from intelligent listening.

These are my views, though. You may be way more advanced than I've credited you here so apologies if my assumption was wrong.

Good luck!

14 hours ago, Kevin said:

What do you think?

 

I think it's a great idea. Almost every composer I know of has trained by copying other people's music. It's all alright so long as it's just for practice.

Score study and imitation is the single best way to learn stuff on your own. No doubt.