Why don't PDFs display all their content in the preview anymore?

[kmatson]

Canvas please help us display all content in a PDF file. We have noticed a subtle but significant change in the in-line preview and the file preview tool NOT displaying all the content of PDF files. We can enhance the PDF file so it displays all the content but when do we need to enhance and why? Is this a permanent change so we need to alert faculty to a process change or will this be resolved?

The in-line preview and the preview in files are not displaying the entire pdf file so students that are counting on that display to be complete are missing content. I have two examples and a good work-around but why is this happening and can it be fixed by Canvas?

Faculty are creating their pdf files in multiple ways but unless they enhance their scan in Adobe their students may not be seeing everything they saw in class if they view in the Files viewer or the in-line preview rather than downloading the file and viewing in Adobe which of course defeats the whole purpose of the preview. Please see both screen shots of this PowerPoint. The second is enhanced in Adobe and views properly in the Canvas file view.

Math writes up extensive notes and takes them to a scanner and this is the result. The file preview many students use doesn't show the entire pdf file. The one on the left is the Canvas preview and the one on the right is the complete view from Adobe Reader.

 

We can fix the pdf files by using Enhance your scan in Adobe but why is this happening, how do we know when we have to enhance the scan? I don't know enough about pdf files to know what or how to anticipate when it will drop content. Does anyone else know?

Thank you,

Karen Matson

University of Oregon

[ericwerth]

Hello  @kmatson .  This is certainly interesting and understandably could cause problems for faculty and students.  I haven't noticed this behavior myself, but also haven't been looking for it so may have missed something.  I see that this question was posted a few days ago.  I thought I would check and see if you learned anything about what is happening or have contact Canvas Support to get their insight.  

Thanks for the update!

[ericwerth]

Hi  @kmatson .  Interestingly, I just noticed something similar with preview files from a PDF in SpeedGrader. I had participants in one of my classes draw and submit images for an assignment and thought I was missing something in the SpeedGrader preview. When I downloaded the file, however, much that was drawn was visible.  This to say, I have even more interest now in learning whether you found a solution! 

[kmatson]

Eric,

Yes faculty can be missing work from students as well. We will be submitting a support ticket since no one has replied. It can be tough to spot but we are seeing it in three classes and very different types of notes as you can see from the two examples.

Thank you,

Karen

[ericwerth]

Thanks  @kmatson , I submitted a ticket after my last response as well.  Here is the relevant part of support's reply.

"...I'm very sorry to hear about the inconvenience of Docviewer PDF documents not rendering all pdf content. To my knowledge typically it does, but it doesn't always render layered pdf's like it should. I've seen them where some student's submissions rendered just fine and others didn't, but they were all filled out if I opened them in Adobe. The work around is to flatten the file after the form has been filled out. 

Open the copy and choose Advanced > PDF Optimizer.

Click the Clean Up tab.

Select Remove Hidden Layers Content and Flatten Layers, and then click OK.

When prompted, save the Optimized PDF with another new name..."

Maybe someone knows of a way to have the PDF flattened automatically upon upload to Canvas.  This would help faculty and students submitting assignments as well.  

[Robbie_Grant]

 @kmatson ,

Were you able to find an answer to your question? I am going to go ahead and mark this question as answered because there hasn't been any more activity in a while so I assume that you have the information that you need. If you still have a question about this or if you have information that you would like to share with the community, by all means, please do come back and leave a comment.  Also, if this question has been answered by one of the previous replies, please feel free to mark that answer as correct.

Robbie

[hasti]

I and my TAs have this problem as well -- my students are scanning their paper submissions to PDFs and uploading them to Canvas and the SpeedGrader does not always display the entire contents. This is a massive BUG in Canvas and needs to be fixed. This question has NOT been answered.

[swind]

This issue is also affecting our users.

The workaround that Canvas support suggested is to resave/convert/enhance the PDF using desktop software, however, this is an incomplete solution since there's no clear indicator to faculty or student that something is missing in the original PDF when viewed in Canvas.

Here are a few relevant notes from my support case.

I've been working with our Level 2 agents who have seen this problem with some PDF files that are uploaded to Canvas. The L2 agent informed me that since PDFs can have complex layers and encoding within them. If there's anything missing in the PDF's code, then the Docviewer may not render the file completely. Reconverting the file allows the external software to convert the file back into PDF which usually resolves the missing bit of code that was causing the Docviewer problems when rendering.

I understand some PDF files are previewing incorrectly in DocViewer. This can happen because of software specific layering, metadata or other configurations in the way the PDF is saved.

Unfortunately, I would not have a way of determining exactly which PDF settings were configured to prevent our previewer from being able to display all the pages.

[swind]

Update, one year later.

It looks like the previous ticket is still with our engineers, and we will reach out to you with any updates we have.

I've requested that this item be added to the Canvas Current Issues page.

https://community.canvaslms.com/community/labs/pages/home 

[govreacl]

HI,

I don't see it on the current issues page when I click the link - do you know the status? It is really frustrating not to be able to have the preview of PDF files like we did before.

[csnider]

I just ran into this problem as well, with PDFs I download from a library ebook.  I have no clue how to fix this.

[bmcgeoghegan]

An earlier comment suggested flattening the PDF and that has worked for images restored in my DocViewer, although the menus in your Acrobat editor might be a little different from Adobe's Help article https://helpx.adobe.com/acrobat/using/pdf-layers.html#merge_or_flatten_layers_acrobat_pro. With or without flattening and then re-uploading, students can select the download and the file still contains the images that don't show in the DocViewer, so it would be great if Canvas can continue a fix.

[elovitt]

Looks like this is something that has been posted a number of years ago and is still being encountered.  My concern like others is with a student submission and when we are supposed to look at downloads instead of the preview?  Also training students and faculty on flattening seems to be a huge challenge!

[csnider]

I ended up printing off the pdf and then rescanning it with office machine.  It was a huge waste of time for something that should just work.

[IEML11]

It is now spring 2022 and it is still the same problem.