I don't understand one thing & I will really appreciate if someone can answer this for me. Suppose, I've made a PDF for my customers and PDF uses either Calibri or Gerogia then will these fonts be available on all platforms? I mean will customers be able to read the PDF that uses Calibri or Georgia on all OSs? Please enlighten me. Thanks.
You should always put a PDF with non-standard fonts through Adobe's "preflight" (it's part of Acrobat) or an equivalent processor. It will tell you if the fonts will be embedded, and an assortment of other useful things.
Unlike web typography, PDFs usually use font embedding to ensure that they display "identically" on all platforms. To do this, some subset of the intended font is included in the PDF file.
Due to this habit, you probably wouldn't think of a PDF as using Calibri or Georgia. It could use one, the other, or both. Font choice becomes a static thing.