To ensure that your publications will run perfectly on Issuu we have set a maximum upload size of 100 MB per document. However, should your PDF exceed this limit, reducing the file size can be done using the instructions below. 

To compress your PDFs, you can use your normal PDF software (e.g. Acrobat, Scribus, or Quark) to minimize the number of fonts, bitmapped images, and (possibly) substitute vector based-graphics with bitmap. Furthermore, consider minimizing the number and complexity of forms in your PDF document and flatten layers. 

Here's a short guide on how to reduce file size by flattening layers in Adobe Acrobat. Learn from it and use the advice to perform similar actions with your favorite PDF software.

1. Open the document in Adobe Acrobat.

2. Flatten all the complex pages into single-layered bitmaps (JPG).

3. Do a text-recognition (OCR scan) before uploading to ensure your document is optimized for search

Done. Also check out Adobe's guide on how to compress your documents.