Highlighting and annotation are processes that involve context as both processes connect a personal addition at a specific location within the source text. Both Zotero and Highlights allow highlights and notes to be exported as a file separate from the original pdf. There are options for the format in which this file is created and one is markdown. A markdown file is a text file that includes a few reserved text symbols that allow the content of the file to appear with headings and subheadings, links, tags, and other such features when opened with a tool that interprets the reserved markdown symbols. Markdown uses such symbols in a way similar to the symbols used in an HTML file. One of the core benefits of a markdown text file is that it will not eventually age out of usefulness. It is a text file and not a proprietary format so there will always be a way to open a markdown file and one does not have to worry about investing years in a tool that creates a file type that may not be useful if the tool is discontinued. 

Here is the useful capability I take advantage of when using these tools on my desktop computer. Having everything on the same machine is essential. Both Zotero and Highlights embed information about the location of highlights and notes within the original document. So, when a note is stored in Obsidian exported from one of these highlighting and annotation tools, a link will be included that will allow the Obsidian user to Zotero or Highlights and show the original text in which the highlight or note was embedded. Zotero is more specific and takes you to the exact location. Highlights takes you to the page rather than the specific location on the page.