Hey Lalit, The use of ''will be sent'' is a fact, it is something that will happen. Those docs will be sent tomorrow no matter what. The use of ''would'' introduces a condition or a doubt. They might or might not be sent. For example: The docs would be sent by tomorrow but they have not been signed yet, so they might not be ready. Other examples: Tomorrow I will go to the party. I would go to the party tomorrow if I had been invited. I will eat sushi for dinner. I would eat sushi for dinner if I weren't allergic to fish. :)

The first expression is stating a simple fact: tomorrow the documents will be ready. In the second phrase, there is a strong doubt that the documents will be ready or it is known that they will not be ready due to some unmentioned circumstance. The second phrase for example could be completed with something like: "The documents would be ready tomorrow, but my computer broke down and all my work was lost."

In your example, you can understand the difference like this: "The documents WOULD be sent by tomorrow morning, BUT..." (You can also use "if" to introduce the next part of the sentence.)