Are you viewing on a phone or a computer?
On a computer, I would right-click somewhere on the page, and choose "Print". You can then choose a printer, portrait vs landscape, colour or black and white etc.
If it seems like it's going to take up loads of pages (it says how many it should take in the print preview screen) I would do this instead:
Select all the text that you want to save, by clicking at the start of the text, dragging your mouse to the end and then only releasing the mouse at the end of this (if that makes sense)
That should "highlight" the text probably in blue. Right-click and choose "Copy".
Open up a word-processing program, like Word, Wordpad, or even Notepad.
Right-click, choose "Paste".
Repeat for any more text that you want to save from the thread.
In the program's menu (probably under File) there should be an option to Print. This will take up less pages as you won't be printing all the adverts etc.