There are many different types of PDF, sometimes due to the way a PDF is saved, when converted into a flipbook using Partica colours can look washed out.
To fix this you need to save your PDF with a different colour profile:
1. Using Acrobat Pro, open the PDF you wish to change.
2. Select Print Production from the tools menu.
3. Select Convert colours.
4. make sure the Conversion Profile is set to Photoshop 5 Default CMYK
5. Click OK to start the conversion
6. Re-save and reprocess the file in Partica