Is there a way to adjust the size of the text when reading PDF files? When I use Aldiko to a book in epub format on a mobile device with a small screen, I can read it without problems. The text is adjustable to the size, the application has no issues.

The opposite is true when I'm reading pdf file. It's always a fight. The text is small and unadjustable and the application freezes.

Is there a way to adjust the size of the text in my PDF files so that they are more easily readable? I don't intend to read scanned pdfs (this would be even bigger fight). I would like to be able to adjust text size, do scaling and not have the application freeze. I'm open to trying other readers if Aldiko cannot handle this.

EDIT: The title was changed, but note that it's not only the change in the size of text. The text should be flexible to various sizes of devices. This is called floating text (or layout) in HTML terminology. A lot of PDF readers can change the text size without the text fitting the device screen.
Use ezPDF Reader and use its text column locking feature in landscape orientation (to kick out blank margins and use large device height as width of PDF). I find it useful on my 4.0-inch screen even for the codes because it doesn't change formatting to reflow text. But, if your screen size is much smaller than my one, it'd be useless to you.
Plus, it features voice reading. You can use that too.