Thanks for posting, I think I know what is happening!
A PDF file is actually a document file, not an image. It sounds like you have an image in the PDF you want to use or you want to use the PDF as the image. For reference, an image file ends in jpeg, png or gif. Since you've uploaded the document it will be in your Library but can only be inserted into your email as a link. I would suggest clicking the Library tab of your account and finding this file.
If you want to insert a link to the document you can by using the "Insert Document link" option. If you want it to show in the email we will need to convert the file to an image or recreate the PDF as the email.
While you cannot insert the PDF file directly into your email, your Constant Contact Library allows you to upload PDF documents that you can link to from within your emails. You also have the option to use the PDF as an image in your email. There are two ways to add a PDF as an image. You can Create an Email from a PDF Using the Third-Generation Editor (Read this FAQ to learn how) and you can Create an Image From a PDF While Uploading to the Library (read this FAQ to learn how).
When you create an Email from a PDF Using the Third-Generation Editor:
Once the template is created, you have full control to add more text content and further customize your branding. Here is an idea of what this process looks like:
You can upload a PDF to Constant Contact and add link to it in your email. There are different steps depending on what editor you are using.
For 2GE users:
Click on the block you want to add the link to. Highlight the text you want to be the link to your document. Once that is done go to the left and you will see ‘Document Link”
If your document:
Then click Insert, click Save and then continue editing the rest of your email, here is the FAQ for this process.
For 3GE users:
Highlight the text you want to link your document to and click Link. Select Document from the Type of link drop-down menu.
Edit the text you want to display as the link. Select a document from your Library. If you haven't uploaded your document yet, just click Upload a New Document to add it to your Library.
Click Insert, click Done and continue editing your email, here is the FAQ for this process.
I hope that helps!