Can Libre Office open PDF's

I have a series of pdf’s that are step by step instruction drawings I want to combine them into one document

If you just want to combine the pdfs then something like pdftk builder will do the job nicely and quickly.

If the layout needs adjusting on the pages then you could open then in draw, make the adjustments, and export to pdf again. You might need to open one and add the other pdfs as new pages one-by-one.

Alternatively, open all in Draw and copy those elements you want into writer

Cheers, Al

PDF Split and Merge is a good option (no LibreOffice software).