Last week I wrote about How to upload a PDF file to Facebook. Because both Facebook and Twitter don’t allow you to directly upload PDF files, instead you need to upload the PDF to a free cloud service like Acrobat.com and then link to the file. However, when posting a link or URL, you may also want to include an image from your PDF file to make the post more visual. You can use Acrobat (not the free Reader) to create an image of any page within your PDF file that you can upload to Facebook or Twitter.
Start by opening the PDF file in Acrobat. If you have more than one page in the PDF, open the Page Thumbnails navigation pane, select the page you want to use, right-click and choose Extract Pages from the context-sensitive menu, and click OK.
In the newly created PDF file, select File > Save As Other > Image > JPEG. Facebook also allows you to upload TIFF or PNG files and Twitter allows you upload PNG files, so you could choose one of these options as well.
Notice the Settings button in the Save As dialog that you can use to further refine your image file.