You can export PDFs from Indesign for a variety of uses, e.g. for printing at high quality, for viewing on a computer screen  or sending over email.

It’s really important to keep in mind what your intent is when making PDFs so you don’t run into problems:

Let’s say you’ve designed a magazine of 70 or so pages and you want to share it with someone over email or DropBox, different export settings can have a drastic effect on the PDF file’s size. One setting might come out at 10MB and another at 650MB.

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It would be impossible to email the 650MB file and it may take forever to upload/download via DropBox!

But the 650MB would be perfect for printing!

The bulk of a PDFs size is in the images. High quality printing requires high resolution images of 300dpi (and large file sizes) while screen viewing only requires 72dpi resolution (and much smaller file sizes).

Indesign offers the ability to create or modify the PDF export settings under File > Adobe PDF Presets >Define:

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Where you can change the image compression settings and save as a preset.  As a rule of thumb, 300PPI for high quality print and 150PPI for screen viewing or sharing.

But here are a couple of ready made presets you could use:

High resolution preset for professional printing (beware of HUGE file sizes!)

Normal resolution for on-screen viewing or uploading

In Indesign, simply go File > Adobe PDF Presets >Define and load the preset file. It will then be available in the preset list under File > Export