This may sound noob question. I have just started exploring pdf modification tools, libraries and software.
I see terms pdf markup and pdf annotations used interchangeably. Software descriptions don't tell which term is what? I have used Adobe acrobat reader DC and Goodnotes to add info to pdf files.
It would be great if you tell me the difference(in technical terms as well) or point me to the right article/document.
I will remove the question if found duplicate.
Many annotation types are defined as markup annotations because they are used primarily to mark up PDF documents
source: Section 12.5.6.2 in PDF32000_2008.pdf
In the PDF specification, a Markup is a type of annotation (one which is visible on the page), but not all annotations are visible on the page, and so not all annotations are markups.
See Table 169 in Section 12.5.6.1 PDF32000_2008.pdf.
Of course any particular library could mean something else by Markup (for instance maybe editing the PDF page content itself (which annotating doesn't edit). But generally markup should mean annotating.