Which version of Acrobat do you have? If it's "Pro", you can use the "Save as Optimized PDF" function to first of all, find out what is taking up how much space in your PDF file (using the "Audit space usage..." function), and then in a second step reduce the file size by selectively removing or compressing information.
The problem dounds like "pages in Photoshop". That's not the starting point for a small file, though it may look very nice. InDesign is the typical choice.
To extend the theme of the previous responders, Adobe Photoshop is an application primarily aimed at producing and editing raster graphics with perhaps some text and vector content. And when creating PDF from Photoshop, the text and vector content within the Photoshop file should be maintained live as opposed to flattening and rasterizing same (which eliminate the ability to downsample and compress the text and vector aspects without severe loss of quality.
If in fact, you are simply producing PDF files that are multiple pages of full-page photos, you obviously need to choose what compromises you make in terms of quality versus file size. Note that the best quality dowsampling and compression for PDF from Photoshop occurs when you save as with the PDF option directly from Photoshop itself, not afterwards!
If you are creating other content such as a book with raster images, you should be using software such as Adobe InDesign for the layout, placing any raster images from Photoshop into the InDesign (for example) document and then exporting PDF. Text and vector content created in InDesign won't degrade based on the compression and downsampling specified during the export.
To reiterate, Adobe Photoshop is not a “Swiss Army Knife” application. It is optimized for raster graphics. If you are using it for other purposes, such as to produce pages of a book, explore use of more appropriate applications!