How do I save a PDF file so that it opens larger?

It’s a viewing option, not a saving option. The people you send to can adjust the magnification in their own viewers.

just tell them to hold down Ctrl and move the mouse wheel up when they view it?

Located in the “Panels” page of Advanced PDF Tools, there is an option to set the page scale to a certain percentage.

EDIT: Sorry, that’s only if you have downloaded that software, which isn’t very good by the way! My boyfriend got it a while back for that very same reason.

An easier way to set the page scale is to go to Properties>Initial View and from there you can set the percentage to 75–80%.

Open your original file, the one you created the PDF from. Before you save it set it to the view setting you want it to open at. Then save it. Unless the default settings have been changed in your program, it should open to the exact view setting you had it at.

It is easy! Open PDF in adobe reader and you will find there are two button on the panel—“pluse” buttion “reduce” button. Click it and you can change the size of characters. or type the number 80% in form beside it.
OK,done.

In your pdf transformer menu (for example i use pdf factory) in docinfo you have magnification button ( here you selected your desired magnification of your pdf view)