Decreasing File Sizes 

Compression and Decreasing your File Size.

Photoshop

Option 1

Make a copy of your images Open Photoshop and Flatten Your images.

This combines all your layers into 1 single background layer decreasing your file size.

Layer>Flatten Image

Then Export/Save As

Option 2

Resize your images in Photoshop before you bring them into Indesign or Illustrator

Image>Image Size

Resize it to match whatever is in your presentation File.

Save As Photoshop PDF

Adobe PDF Preset:High Quality Print

Compression

Set Your Downsampling to 150ppi (Pixels Per Inch) For Images above 225 PPI

Save PDF

Acrobat Pro DC for PDFs

Tools>Optimize PDF>Advanced Optimization>

Downsample to 150ppi

Image Quality to High

Export

Using Indesign

File>Export>Adobe PDF

Adobe PDF Preset:High Quality Print

Compression

Set Your Downsampling to 150ppi (Pixels Per Inch) For Images above 225 PPI

Compression Automatic JPEG

Image Quality: Maximum (If your file size is still too much decrease this to High)

Export

If after all this your file is still too large change your Downsampling to 100ppi

This is a useful video guide on how to do this in InDesign

If you file save size is too small or you lose too much quality just bump things back up

slightly.