Which sentence is correct and why? What is the difference in meaning?

  1. I have already written to you, and I received your reply to submit my documents.
  2. I have already written to you, and I received your reply in order to submit my documents.

Solution 1:

Both are generally accepted as the same; however, many styles would regard 'in order to' as needlessly wordy. As a technical writer, I search documents for phrases like 'in order to' or 'make use of' and change them to 'to' and 'use' respectively.

tl;dr – The second sentence is better, but no more "correct" than the other.

Solution 2:

I agree with aeismail's answer. However, I might add that they never really mean the same thing. It is simply the case that the difference in the shade of meaning that they convey is oftentimes not terribly critical. Occasionally it is critical, as in the case above.

Generally "...to...", introducing a purposive clause, is used to outline an intended course of action:

Q: What happened?

A: I received a reply to submit my documents

Consider also: 'I plan to do it.'(okay) versus 'I plan in order to do it.'(yuch!)

On the other hand, "...in order...", introducing a rationale clause, is used for explanations, justifications or necessary causational relationships:

Q: Why did you receive a reply?

A: I received a reply in order to submit my documents

Consider also a headline I just came across from Medical News Today: "Brainwaves converge in order to learn". [http://www.medicalnewstoday.com/articles/278195.php] The explanatory meaning in the headline takes obvious precedence, and the headline is somewhere between awkward and unacceptable without "...in order..." in the sentence.