Hello,
When using Start Process activity, the FileName property should point to the adobe executable (in my case Adobe Acrobat Reader DC, so AcroRd32.exe) and then in the Arguments property you can put your pdf parameters, precedeed by “/A” and followed by the path to the .pdf file. Here’s a capture with the activity:
Edit: As for Open Application activity, the FileName property is the same as above and the Arguments property is the same but with the executable at the beginning of the string (“AcroRd32.exe /A…”). The “title” attribute of the Selector property should be modified to the title of the .pdf file as it appears in the upper-left corner when the file is open (e.g. “file.pdf - Adobe Acrobat Reader DC”), or you can also use wildcards for something less specific. Here are captures with the properties: