Hello there Oracleeduta,
We understand that you're not able to see photos at times when you open PDF documents via the Files app, so let's look into this in more detail.
Are you saving these PDF documents to the Files app on your iPad, or are you saving the documents via a different device to Files? If you're saving to Files from a different device, are you able to see the photos there?
In addition to that question, if you close the PDF then open it again after viewing, does the photo appear at that time? Also, have you tried connecting to a different Wi-Fi network to see if this may be related to slow download speeds?
Check out the following resource for additional information on using the Files app to see if this may be related to the file type not being compatible as well.
Use the Files app on your iPhone, iPad, or iPod touch
We hope this is able to help, and look forward to hearing back from you.
Cheers.