There is no inherent reason why Word 2010 cannot produce a PDF file in which text can be selected:
The PDF function in Office is quite rudimentary and does not include the security options of some PDF tools, notably Acrobat and PDFCreator. A document that comprises simple text (and not an image of text), as apparently does yours (and mine certainly does)
is the simplest form of document for PDF creation, which suggests that the problem lies elsewhere. Perhaps a display driver issue?
Word can behave oddly with custom page sizes and yours looks an unusual size. Is it the same result with a standard page size?
Your question begs another. Why are you converting to PDF if you intend that the text can be selected? PDF is a graphical representation of the document and is often used to limit editing and deter plagiarism. It can never succeed in either, but it does
make it less convenient for others to copy.