The problem is that the word 'absorb', which is the root of both 'absorbed' and 'absorbing', is a verb but 'absorbing' in this case is an adjective. The reason you don't use 'absorbed' in the sentence you have is that you want an adjective to describe the writing, not refer to the writing actively 'absorbing' someone. Similarly, 'engrossing' is not about the process of engrossing (verb) but is used to describe the writing (adjective).
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NakoolIn the above sentence, there should be 'absorbing' in place of 'absorbed'.Correct.
NakoolIs there any rule?The rule is to use the word with the correct meaning. You can look up meanings in a dictionary. I found these in an online dictionary: