You can use Okular, of course: print to file -> the pages you want. But thus you get an image pdf. If you want keep a text pdf, you can use a program like PdfArranger, which allows to save (only) the pages you want from a whole pdf, keeping them as searchable pdf (text).
re-ocr a pdf with Adobe
You have to 1) save the old searchable pdf to tiff images (as many as the pages), 2) ocr the tiff images to a searchable pf 3) combine the new multiple pdf to one pdf.
manage pdf online
Excellent websites are https://www.sejda.com/ (with the only limit of three works per hour, regardless to the pdf pages number) and https://tools.pdf24.org/ (with no limitations, but with less features than the first one).