resolution too high to upload to cloud

[elizabeth@alextechmetro.com]

Some time ago, I scanned a large batch of documents and created PDFs for uploading to the cloud, but then realized that I had scanned at too high a resolution and they were too big to upload.  I rectified this with future scans, but I have hundreds of very large PDFs that I still want to upload.  Does anyone know if I can lower the resolution of an already existing PDF? 

[Bernd Alheit]

Possible with Adobe Acrobat, not Acrobat Reader.