Here are my two cents (probably worth less than that).
What is property, except what a social community agrees is such? At least in the United States, the government (as constituted by the people, at least in theory) has decreed that there exists a thing such a private property (not a necessary conclusion, see, for example, the former USSR). The government, again, representing the people, has defined what that property is. Because of a need to stimulate creativity by making sure that people will spend their precious time inventing something new, and not fearing that their time will be wasted in an economic sense, the Constitution gives Congress the power to create patents, trademarks, etc., so that those people can make money from their original ideas. The government has established copyright laws, which have changed over time, to represent what should be protected.
President Clinton, working with the Congress, made sweeping changes to the Copyright laws of the United States. That which you have written, and which is an original idea or thought, is copyrighted. Here is a nice summary of copyright terms written by people who actually study this sort of thing:http://copyright.cornell.edu/resources/publicdomain.cfm
So depending on when the book you have is published, it might still be under copyright. If it is, and if you buy the book, you can make an additional copy for your own use, not to share with others. Others have to buy their own. "Fair use" means generally that you can copy a snippet or a few pages of something that you might quote in an article, book review, etc., adding to what is already there.
The above is not a legal opinion, it is my synthesis of the facts as I know them without thorough research.
Because government establishes what is property -- they establish whether you can buy land for yourself or whether it is a public park, for example -- I believe that taking something within their definition of property constitutes stealing. It might be more anonymous than stealing a tree from a public park, but the principle is the same.
If you disagree with the boundaries on property, and think the government screwed up their economic calculus for copyright (i.e., you think that sharing information after a fewer number of years or with less restrictions would be more advantageous), your responsibility as a citizen is to petition the government with your reasoning and ask them to amend the law, and convince others to do the same.
I have seen firsthand the emerging countries of Eastern Europe which have, not surprisingly, no respect for private property such as expressed in copyright laws. Their people copy and take whatever they want. And they wonder why innovation is slow there, and they always are importing western movies and even their TV shows are often copies of (poor) American shows, expressing little cultural originality. I put some of the blame on this issue, at least; if someone can't make money doing something, they just won't do it. You can't blame them, because they, too, need to eat. And if you think they're making too much money, the answer, in my view, is not to steal from them, but to argue that society accept your conclusion so that a fair result might be attained.
I know that other countries have wildly different systems. But my thoughts here are assuming that you're in the USA, with the assumptions underpinning our governmental system being what they are.