This is the 5364th most frequent Russian word.
отправкой
"Отправкой" means "sending" or "dispatching."
In this sentence, 'отправка' is used as a noun referring to the act of sending documents.
Его отправка документов была неожиданной.
His sending of the documents was unexpected.
Here, 'отправка' is again a noun, referring specifically to the sending process related to the package.
С отправкой посылки возникли проблемы.
There were issues with the sending of the package.
In this example, 'отправкой' is used in the instrumental case as a noun indicating the means by which he is engaged in an activity.