I've been working with PDFs and found an easy way to move PDFs into a container field if you have only the reference in a container field.
For example, rather than use FileMaker to store the PDF you left it on a drive and referenced it but now want to store it in FileMaker.
The first assumption is that the import was properly done and the second is that the files are still where they are referenced.
When you import a file the import dialog points to these fields: Image, File Name, File Path and Image Thumbnail. Create these and the Image fields are Containers, the File fields are text.
When you import a folder full of PDFs FileMaker does all of the work for you and in the File Path field gives you the path to the file. Of course you set the import for Reference Only.
Now, you want to bring the PDFs into FileMaker. Easy...
Use Insert From File and the FilePath after you add a third Container field which I have above "Image Inserted...."
You can script the process with a substitution as shown below. Mac would use filemac and from anothe computer would need the network path substitution.
That's all you need to insert a PDF from a container with a reference only.
If you don't have the File Path field, that's a different discussion.
Wrap a loop around this and you can import thousands and thousands of records (melting your hard drive, cpu and router...).