For my future reference, in case I ever get this error message again—the steps in solution 1 on this page worked for me! https://helpx.adobe.com/au/acrobat/kb/bad-parameter-while-deleting-pages-in-acrobat.html
In case that page ever goes missing or gets relocated, here’s the summary of the steps that worked for me in my Acrobat XI Pro version, with some minor edits by me:
Combine the PDF with another PDF
- Before you start, create and save a blank, single-page PDF from Word, or some other program.
- Launch Acrobat, and then choose File > Create > Combine Files into a Single PDF.
- Click the Add Files menu and choose Add Files.
- Browse and select the PDF file that shows the ‘Bad Parameter’ error, and then click Open.
- Click the Add Files menu and choose Add Files.
- Browse and select another PDF file, preferably the blank one you created at Step 1, and then click Open.
- Click Combine or Combine Files. The selected files are combined into a single PDF, and the file (Binder1.pdf) is opened in Acrobat.
- Save the file. Select all the pages you added to the PDF using the Combine Files operation (the pages of another PDF you selected while combining files). Delete the selected pages:
- In Acrobat DC/2017, choose View > Tools > Organize Pages > Open. Select the pages you want to delete, and then click the Delete icon or press Delete.
- In Acrobat XI, choose View > Tools > Pages. Select the pages you want to delete, and then click Delete in the right pane or press Delete.
- Save the file again. To see if the error still occurs, try to delete a page from the PDF.
[Link last checked May 2021]