If you have iPod Touch, you can use iBooks to read PDF files but if you have an older-generation device, you can also read PDF documents in your iPod but only the text, not the embedded images.
Here's the three step process to turn your iPod into a basic PDF viewer:
1. Open the PDF document in Adobe Reader and save that as a text file. Alternatively, you use GMail or Zamzar to extract the text out of the PDF.
2. Next upload the text file to ipod-notes, give it a name and download the split version as a Zip. [can also be used for saving HTML web pages to your iPod like articles from Wikipedia]
3. Plugin your iPod and Enable Disk Use in iTunes. Now open Windows Explorer and double click the Notes folder in iPod device. Just extract the zip file here that we created in Step 2.
To read the PDF on your iPod screen, scroll to Extras -> Notes. All notes are automatically connected with each other just like hyperlinks in websites.