Quote marks are backwards (using texmaker/PDFLatex)

LaTeX tends to require you to use

`` '' 

for double quotes and

` '

for single quotes. The "smart quotes" will be done by the compilers.

if you have already typed your text with " " throughout your document you can use the csquotes package to deal with them:

\usepackage [english]{babel}
\usepackage [autostyle, english = american]{csquotes}
\MakeOuterQuote{"}

Adding this to your preamble will use the double quotation mark character as your delimiter for outer quotes. csquotes will then translate it to what it needs to be in your chosen language, which in your case is american english and so will appear as “ ”. You should therefore have nothing else to change in your document.

Opening quotes are `` and closing quotes are ". For instance,

\documentclass{article}

\begin{document}

``Thanks!"

\end{document}

For greater control over your quotations (in particular, for your concrete "search and replace" problem), you could consider using the csquotes package:

\documentclass{article}
\usepackage[english]{babel}
\usepackage[autostyle]{csquotes}

\begin{document}

\enquote{Thanks!}

\end{document}