Thanks John but there is nothing in the "fonts to outline" section of the Fonts tab. I still cannot select text in the pdf file. I am using version Scribus 1.3.3.14 and the OS is Windows 7 Professional
I am beginning to feel this is a tool limitation in Scribus 
It's not a limitation of Scribus, but it might be a limitation of the font(s) you are using. Although unusual these days, some fonts contain a "do not embed" flag that the developer added in order to stop piracy. Scribus will recognize that flag and refuse to embed the font, although I think you can override that with Meho's suggestion.
Some definitions may help:
Embed: Place into the PDF a copy of every glyph contained in the font together with all the font information. There are tools that can extract an embedded font from a PDF, which is why some developers have set the "do not embed" flag, even some developers of open source fonts. Adobe did this briefly, but they got yelled at so loudly that they no longer do it. It is unlikely that the fonts you are using have the "do not embed" flag set, but don't rule out the possibility.
Subset: Place into the PDF every glyph and the font information for them, but only for glyphs actually used in the document. Some PDF creator applications allow you to specify a percentage of the glyphs instead of all the glyphs used in the document.
Outline (also "convert to paths"): Convert all the glyphs into vector images. The advantage is that this eliminates any possibility of the PDF failing to print because of a missing font, plus it makes the PDF file much smaller. However, as you have discovered, the text is no longer text and cannot be selected.
A few things are clear:
1) Scribus certainly can, and normally does, embed fonts. I've done it for years and the text in the PDF is selectable. That your text is not selectable in the PDF is proof that Scribus converted the fonts to outlines. Why and how to make Scribus embed the font instead are the questions.
3) The version of Scribus you are using is really old. The current development version (1.4.0 RC5) is almost ready to be released as the next stable version. I would recommend you install it to take it for a spin. I use it now for production work (but I save often, just in case). You can install 1.4.0 RC5 alongside 1.3.3.14. But having suggested that I must caution you that the file format has changed for 1.4.0. Version 1.4.0 can open 1.3.3.14 files, but not the other way around. So before opening an existing file in 1.4.0 make a copy of it with you file manager (Windows Explorer).
I would also suggest opening a new, blank document and create some text frames, but use different fonts. This is just an experiment, so just create random frames with random text. Export to PDF and see what shows up in the fonts tab of the PDF export dialog box. Finish the export and see if any of the text is selectable in Adobe Reader.
And speaking of Adobe Reader, it has a feature that will tell you what fonts are embedded or subsetted in the document. I'm betting that for the PDF where your text is not selectable it will indicate no fonts.
That was a lot, but hopefully somewhere in the above you will find a way to figure out what is going on and how to remedy the situation.