If you are unable to select or highlight specific text in a PDF document in Adobe Acrobat Reader on Windows, this post will help you fix it.

If you want to extract highlighted text from PDF file as a plain text file, then this post covers some good free PDF Highlight Extractor software to do that.

ReaddleDocs’s PDF viewer now lets you highlight text inside PDF files in several colors, make notes at any place in the document, and save these changes in a desktop-compatible PDF format.

To see alt text in a completed PDF document, you'll need to use a screen reading app, which is an accessibility tool for visually impaired users.