I think you mean, increase the text size only, right ?
I don't think there is a perfect solution to do that, once a pdf is already made. That is, you can't enlarge the text separate from the entire pdf.

When you go to Print, most print drivers (the dialog box that comes up) allow you to "scale" the page - make it larger or smaller - so that might help a bit.

But that will enlarge the entire page. If you scale it large enough, eventually you will enlarge the pdf over the margins, to more than one page, which is probably not what you want.

Of course, if you're generating a pdf from a Word doc, whatever, you'd increase the font size before you made the pdf.

I should have mentioned, perhaps your default settings are printing at less than 100% already, and that's the source of the problem. Make sure when you go to Print, it's already set at at least 100% or "Print to Margins", something like that.

On my Canon software there is a checkbox for "Preview before Printing", which allows you to see what's going to happen before it's actually going to print - saves a lot of paper when experimenting.

yes, kbarb, that is what I am after, when I do my own pdf's I make print large, can make smaller but those I receive, well doggone it is hard sometimes to make it out. I hadn't thoght of the print to margin thingy, that is good info to have. I try even for 200 sometimes, and that preview doesn't always give a good preview, but is better than wasting the ink I guess.
What if I took a picture of the text, as in the Edit part of the pdf, put into paint and enlarged, would that be any better ya think? Is the only real solid thing that I can think of, and as I need text a lot for some of my work,
could help maybe?

I assume you just have a pdf viewer. In the standard version you can use tools to edit text and change font size.

In a pinch you could change the view size and then do a print screen and then paste into a graphics program then crop and print.

Most likely the problem you're having with Preview, is that you've enlarged the pdf so large that parts of it are now on new pages - pg2, pg3, etc - which is why it doesn't look right.
But since it doesn't look right, then you can decide not to print and try a diff scale - saving some ink and paper.

I don't think you can enlarge the text separate from the whole page - like in a word processing program - it all enlarges as a whole.
The trick is to enlarge/zoom as much as possible, but still have it print on to one page.

I don't know what pdf viewer you're using.
But with Foxit Reader that I'm using, there is a "Snapshot" function on the Home tab, where you can outline a selection of the pdf, and print just that. But that's probably not a great solution either, although it's an easier way to do your print screen idea.

Also . . .
There is the print dialog box that pops up upon Print, and then on that dialog box, there is the printer's own driver dialog box that you get when you click "Properties" next to the selected printer (up at the top).

Some of those Properties have features where you can print as a poster, banner, etc., but that would probably be unwieldy and take a lot of experimentation. The idea would be to try and print a page of a pdf - but enlarged, and over a number of pages in some kind of orderly fashion.