When I copy and paste in LibreOffice a text from, say, the internet, I find that extra spaces are inserted between paragraphs. Is there an easy way to eliminate these en bloc, as one can do in MS Word?
extra spaces are inserted between paragraphs.
Depends on what extra spaces exactly means (empty paragraphs?). Could you upload a sample file?
Text from the Internet may get space added below and above the paragraph, you can see that in Format - Paragraph - Indents & Spacing.