There are two methods for bringing documents into OJS for publishing:
- Going through the regular submission process
- Using the Articles & Issues XML Plugin (Import/Export)
If you want to use the first method but don't have the original .DOC file, you can go ahead and submit the document as a PDF; there's no requirement for the submission file to be any particular type.
However, if you're not going to use the Review, Copyediting, Layout Editing, and Proofreading features of OJS, it's probably going to be faster to use the second method (Import/Export plugin). This is designed for batch imports, but you can use it for single documents if you like. To use this, you'll have to create an XML document conforming to plugins/importexport/native/native.dtd in the OJS distribution (2.0.1 or newer).
Currently, there's no more direct method to import PDFs for publishing. The OJS team is considering this for a future release.