I am not a lawyer, but here are some basic thoughts and suggestions:
Maybe I can send the Word file to my email account as basic proof that I wrote the text first?
You could, but I would not rely on this. International copyright protection can be a bit complex, but for most copyright to apply you have to "publish" you work or otherwise make it available to the public. The simplest way to do this is putting it in a physical form. I would suggest printing at least two copies of the final work and/or perhaps putting the work on multiple dated CD/DVD ROMs. Paper is likely a safer bet. Put an offer somewhere on the internet (where you can point to later if need be) to allow people to "buy" them (or maybe print a few dated "order forms").
I also would make sure to use a copyright symbol in your final work to help satisfy the Universal Copyright Convention.
Whenever Amazon "publishes" your work, this might count for copyright as well, but this may not be as reliable in the United States:
From Wikipedia - Berne Convention
"In the internet age, unrestricted publication online may be considered publication in every sufficiently internet-connected jurisdiction in the world. It is not clear what this may mean for determining "country of origin". In Kernel v. Mosley, a U.S. court "concluded that a work created outside of the United States, uploaded in Australia and owned by a company registered in Finland was nonetheless a U.S. work by virtue of its being published online". However other U.S. courts in similar situations have reached different conclusions, e.g. Håkan Moberg v. 33T LLC. The matter of determining the country of origin for digital publication remains a topic of controversy among law academics as well."
Remember that country of origin can affect how international copyright is applied.
Below are some links and excerpts to consider regarding "physical" publication:
From Copyright.gov (United States)
"There are two principal international copyright conventions, the Berne Convention for the Protection of Literary and Artistic Works (Berne Convention) and the Universal Copyright Convention (UCC).
An author who desires copyright protection for his or her work in a particular country should first determine the extent of protection available to works of foreign authors in that country. If possible, this should be done before the work is published anywhere, because protection may depend on the facts existing at the time of first publication.
From [Wikipedia - Publication] 1
"In the Universal Copyright Convention [UCC], "publication" is defined in article VI as "the reproduction in tangible form and the general distribution to the public of copies of a work from which it can be read or otherwise visually perceived."
More from Wikipedia - Berne Convention
"Under Article 3, the protection of the Convention applies to nationals and residents of signatory countries, and to works first published or simultaneously published (under Article 3(4), "simultaneously" is defined as "within 30 days") in a signatory country."
From the Berne Convention Article 3
"(3) The expression “published works” means works published with the consent of their authors, whatever may be the means of manufacture of the copies, provided that the availability of such copies has been such as to satisfy the reasonable requirements of the public, having regard to the nature of the work. The performance of a dramatic, dramatico-musical, cinematographic or musical work, the public recitation of a literary work, the communication by wire or the broadcasting of literary or artistic works, the exhibition of a work of art and the construction of a work of architecture shall not constitute publication."