A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi A Yung,
Thank you for posting your question in this community. Based on your description, you are using File viewer webpart to display some of your PDF documents. However, it seems that some of your PDF files cannot be displayed correctly as the size of the PDF documents may not able to fit into the webpart.
I understand that it would be quite convenient to directly edit File view webpart in order to resize the page to display. A lot of users also noticed this limitation with File view webpart and raised an idea about File Viewer web-part needs view-size option, which it can allow user to custom the display size in File viewer webpart. If it is convenient, you can vote and subscribe this idea. As more and more people vote on this idea. It can let the related team be aware of this limitation and improve it with a better solution in the future. Thank you for you understanding.
At meantime, here is a workaround I think you can give a shot, which you can use embed code to embed PDF document with Embed webpart with below code:
<iframe width="500" height="500" src="Your PDF file link here "></iframe>
You can change the width and height number to adjust the size to display PDF file. And paste your SharePoint PDF file link into “Your PDF file link here” section.
The output in the embed webpart will look like below:
Best regards,
Dihao