A PDF-1 file is a .PDF file that has been renamed from .pdf to .pdf-1. It is saved in the PDF format, which is commonly used for storing documents and publications in a standard format that can be viewed on multiple platforms. PDF-1 files are typically renamed to indicate that they are the first or second PDF in a series of PDF files.

PDF-1 files may be opened by renaming the .pdf-1 extension to .pdf, then opening the file with a program that supports PDF files, such as Adobe Acrobat, Google Chrome, or Apple Pages. If you need to rename the PDF file as a PDF-1 file after opening the file, simply change the .pdf file extension to .pdf-1.