Hi Anne Boss 

Unknown said:

I have a pdf file with many images and once in Trados, the letter are so small that it's very inconfortable to read.

Why don't you turn off the wysiwyg mode in Studio and then you can keep all the text the same size in the Editor and even make it larger if you want?

https://multifarious.filkin.com/2015/03/11/adjusting-the-view/

If that works your best solution is probably this:

1. Open the PDF in Trados as a single file
2. Immediately close the file after it opened
3. Look in the folder where the source PDF was and now you'll have a DOCX
4. Tidy up the DOCX and translate that instead

Also make sure you are using IRIS for the PDF conversion:

https://multifarious.filkin.com/2017/08/17/iris-ocr/

Unknown said:

I copied the source text into an Excel file and will translate it in Trados. But how can I keep the translation and insert it in the original source text (with the images)?

If you persevere with this approach then you'd have to recreate the PDF as a Word file anyway and then edit that.  So I'd recommend the process above.  Only other way would be a PDF editor but I think that would be a massive waste of time.