To select text click on the “Text Select Tool” (the icon on the PDF toolbar that’s a capital “T” with a dotted square next to it), then click and drag as you would in a word document or web page. To copy the selected text, click on the “Copy” icon (Ctrl-C won’t work, and neither will the copy and paste tools on the menu of your web browser, as opposed to the PDF icons on the lower toolbar). The “Copy” icon is the icon on the PDF toolbar that looks like two sheets of paper on top of each other, with the top sheet offset below and to the right of the bottom sheet. (Actually, the “Text Select Tool” is pretty much selected by default, unless you’ve clicked on another PDF icon, such as the “Zoom In Tool”, which is the one that looks like a little magnifying glass.)
Once the text has been copied, it should be in your clipboard, and can be pasted into documents, “Submit Reply” boxes, etc. with Ctrl-V (or the “Paste” item on the “Edit” menu, if you prefer).
(Some of that is assuming that you’re using Internet Explorer, which you may not be; however, the PDF file-specfic commands–the selecting and copying of text–should pretty much work no matter what platform you’re on, that being the point of PDF files in the first place.)