Repeat title rows at the top of each page as suggested by Travis. Now every page has the same header.
In Acrobat Reader, select View > Page Display > Single Page View
At the same time, scrolling is de-selected. So, the visible part of the page never changes. While scrolling through pages, which all have the same header, it appears as if the header is frozen and the content below the header scrolls. But that's an optical illusion. If you look closely, you'll see that the screen content changes one page at a time, not one row at a time, so it's paging rather than scrolling. With the header in a fixed position, the illusion is almost perfect.
It is not an Excel setting, but an Adobe Reader setting. I don't know if this setting can be manipulated from Excel, or if it requires a PDF creator like Acrobat.