First question: if you open or import the PDF without open or change anything with Acrobat, are you able to open the PDF correctly?
The second question would be what kind of modifications does it make. If it's about filling out forms, for example, that may be the explanation.I frequently open files in CorelDRAW that have been saved in Acrobat Pro, in different versions, so that shouldn't be a problem. So I think that is not the cause of the problem. Maybe if you used a very new version of Acrobat and a very old version of CorelDRAW, but I think that is not the case.
Remember that not all PDFs are created equal, despite using the same file extension. You have a series of options, some are already pre-defined, such as PDF / X1a, PDF / X3, PDF / X4, etc. but you can modify them and create new custom ones.That is what explains that one PDF works well and another does not, and also that one converts the text to curves. These are options selected when saving as PDF or printing as PDF.
I suggest you try some, for example PDF / X3 or PDF / X4.Another option would be to choose "save as / optimized PDF" and discard additional non-visible information, flatten layers, embed fonts, etc.In case I can't solve it, feel free to send it to me at ariel.garaza@gmail.com and I'll check it