In Finder, some of my PDF icons appear as the following, with a black binder graphic down the left side:
Other icons appear without the binder:
Most PDFs seem to start out with the binder when first created or downloaded, but it then disappears from some. What is the reason for this? How can I keep the binder icon all the time so my files are consistent?
MacBook Pro 13”, macOS 10.15
Most PDFs that I have feature the "binding" icon treatment, regardless of the creation software. There are exceptions.
PDFs exported from Apple's Pages do not have this icon binding treatment, and neither do some PDF v1.5 documents. Another example is a PDF generated by PDFTex using the hyperref package. Paper scans from VueScan to PDF will not have the icon binding either. And I have one PDF here exported by InDesign CS6 which lacks the icon binding too.
One possibility is that you are using two different PDF apps each of which creates a different icon. The other possibility is that the second icon represents a one-page document or, perhaps, a two-sided document.
Is there anyway I can stop it disappearing?
No. This will be a function of how the particular PDF content is written to disk, and what method the writing application chooses to generate the icon thumbnail.
PDF Icons Aren't Consistent
