Do calling \includepdf make the page dimension of output equal to that of the included document?

By default pdfpages respects the page size of the surrounding document. But you can use the fitpaper option to force the size.

\documentclass[]{article}
\usepackage{pdfpages}

\begin{document}
some text
\includepdf[pages=-,fitpaper]{example-image-duck.pdf}
\end{document}

The page size will remain whatever is specified by the document class, or adjusted size specified using the geometry package or some direct method.

The size of the included pages will remain as the original unless an adjustment is made (and I'm not sure how to do that).

If the pdf pages are larger than the (perhaps adjusted) class-specified size, you will get warning or error messages in your log.

Although the "overage" of larger pages will probably appear when viewed on screen, unless that is larger that the specified paper size, whether or not (and how) they might be cropped in printing depends on the pdf reader being used.